Write Compile and Run Your First Java Program

Reference documentation tells you what the platform exposes; this lesson focuses on how to reason while using it. The example is intentionally small enough to inspect completely, but the decisions are the same ones that appear in larger Java systems. The specific test here is about Compile and Run Your First Java Program: change one relevant input, configuration value or boundary and make sure the result still matches the contract described above.

In this lesson

• Place Compile and Run Your First Java Program in the context of the First Program module rather than treating it as an isolated feature.
• Build a mental model for what happens before, during, and after the operation.
• Work through a reproducible example connected to the scenario: build a small domain application that grows into tested Spring-backed services.
• Inspect the result and distinguish evidence from assumption.
• Recognize failure modes, misleading shortcuts, and production constraints.
• Leave with a verification checklist and a practical exercise rather than a memorized snippet.

Verification checklist

For a Java developer, Compile and Run Your First Java Program becomes useful when it changes a decision you can verify. The learner should be able to describe the inputs, the operation, and the result in plain language. In the running scenario—build a small domain application that grows into tested Spring-backed services—the input might be a value, request, record, event, configuration setting, or user action. The operation is the part controlled by Compile and Run Your First Java Program; the result is the state you can inspect afterward. Keeping those three pieces explicit prevents the lesson from collapsing into memorized commands. In this lesson's Compile and Run Your First Java Program example, record the evidence you observed rather than treating the rule as a slogan; that note becomes useful when the next First Program exercise changes the conditions. In Java lesson 7 — Write Compile and Run Your First Java Program, use that observation as the checkpoint for this exact First Program topic rather than generalizing it beyond the evidence.

The practical question behind write compile and run your first java program is not simply whether the feature exists, but what behavior it gives you control over. Documentation often presents the API or syntax first because reference pages are written for lookup. A tutorial has a different job. Here the explanation begins with intent, then shows the smallest concrete implementation, then adds constraints. That order lets you understand why a setting or line exists before you are asked to remember its spelling. The specific test here is about Compile and Run Your First Java Program: change one relevant input, configuration value or boundary and make sure the result still matches the contract described above. In Java lesson 7 — Write Compile and Run Your First Java Program, use that observation as the checkpoint for this exact First Program topic rather than generalizing it beyond the evidence.

What this first build prepares you for

Before adding more syntax, make the state of the system observable. That habit matters especially when working with Compile and Run Your First Java Program. The learner should be able to describe the inputs, the operation, and the result in plain language. In the running scenario—build a small domain application that grows into tested Spring-backed services—the input might be a value, request, record, event, configuration setting, or user action. The operation is the part controlled by Compile and Run Your First Java Program; the result is the state you can inspect afterward. Keeping those three pieces explicit prevents the lesson from collapsing into memorized commands. The specific test here is about Compile and Run Your First Java Program: change one relevant input, configuration value or boundary and make sure the result still matches the contract described above. In Java lesson 7 — Write Compile and Run Your First Java Program, use that observation as the checkpoint for this exact First Program topic rather than generalizing it beyond the evidence.

There are usually several ways to accomplish the same visible result. The important skill is knowing which guarantees differ when you choose one form of Compile and Run Your First Java Program over another. Documentation often presents the API or syntax first because reference pages are written for lookup. A tutorial has a different job. Here the explanation begins with intent, then shows the smallest concrete implementation, then adds constraints. That order lets you understand why a setting or line exists before you are asked to remember its spelling. The specific test here is about Compile and Run Your First Java Program: change one relevant input, configuration value or boundary and make sure the result still matches the contract described above. In Java lesson 7 — Write Compile and Run Your First Java Program, use that observation as the checkpoint for this exact First Program topic rather than generalizing it beyond the evidence.

Questions to answer about Compile and Run Your First Java Program

1. What is the smallest input or state that makes Compile and Run Your First Java Program observable?
2. What does success look like, and how can you prove it without relying on a vague UI message?
3. Which configuration, permissions, types, versions or environment details can change the result?
4. Which failure is most likely for a beginner, and what evidence distinguishes it from a different failure?
5. What should remain true after the example is repeated, automated or moved to another environment?

Define the smallest useful outcome

In the First Program part of this learning path, Compile and Run Your First Java Program is deliberately introduced now because later lessons depend on the boundary it establishes. The learner should be able to describe the inputs, the operation, and the result in plain language. In the running scenario—build a small domain application that grows into tested Spring-backed services—the input might be a value, request, record, event, configuration setting, or user action. The operation is the part controlled by Compile and Run Your First Java Program; the result is the state you can inspect afterward. Keeping those three pieces explicit prevents the lesson from collapsing into memorized commands. Keep this point tied to Compile and Run Your First Java Program. The same general engineering habit appears elsewhere, but the evidence and failure signals in this First Program lesson are specific to this mechanism.

A production system rarely fails at the exact line shown in a beginner example, so this section connects Compile and Run Your First Java Program to the surrounding runtime and operational context. Documentation often presents the API or syntax first because reference pages are written for lookup. A tutorial has a different job. Here the explanation begins with intent, then shows the smallest concrete implementation, then adds constraints. That order lets you understand why a setting or line exists before you are asked to remember its spelling. For Compile and Run Your First Java Program, apply this check in the context of the First Program workflow before carrying the assumption into later Java work.

Build the first version deliberately

For a Java developer, Compile and Run Your First Java Program becomes useful when it changes a decision you can verify. The learner should be able to describe the inputs, the operation, and the result in plain language. In the running scenario—build a small domain application that grows into tested Spring-backed services—the input might be a value, request, record, event, configuration setting, or user action. The operation is the part controlled by Compile and Run Your First Java Program; the result is the state you can inspect afterward. Keeping those three pieces explicit prevents the lesson from collapsing into memorized commands. Keep this point tied to Compile and Run Your First Java Program. The same general engineering habit appears elsewhere, but the evidence and failure signals in this First Program lesson are specific to this mechanism.

The practical question behind write compile and run your first java program is not simply whether the feature exists, but what behavior it gives you control over. Documentation often presents the API or syntax first because reference pages are written for lookup. A tutorial has a different job. Here the explanation begins with intent, then shows the smallest concrete implementation, then adds constraints. That order lets you understand why a setting or line exists before you are asked to remember its spelling. For Compile and Run Your First Java Program, apply this check in the context of the First Program workflow before carrying the assumption into later Java work. In Java lesson 7 — Write Compile and Run Your First Java Program, use that observation as the checkpoint for this exact First Program topic rather than generalizing it beyond the evidence.

Evidence table

What you inspect	What it tells you	What it does not prove
Source/configuration for Compile and Run Your First Java Program	What you asked the platform/runtime to do	That the request actually succeeded
Build/validation output	Whether static checks accepted the artifact	That production data and permissions behave correctly
Runtime/result output	What happened for this input	That every edge case is safe
Logs/diagnostics	Where the system spent time or failed	The root cause without interpretation
Repeat test	Whether behavior is reproducible	That the design is optimal

Understand every file that appeared

Before adding more syntax, make the state of the system observable. That habit matters especially when working with Compile and Run Your First Java Program. The learner should be able to describe the inputs, the operation, and the result in plain language. In the running scenario—build a small domain application that grows into tested Spring-backed services—the input might be a value, request, record, event, configuration setting, or user action. The operation is the part controlled by Compile and Run Your First Java Program; the result is the state you can inspect afterward. Keeping those three pieces explicit prevents the lesson from collapsing into memorized commands. Keep this point tied to Compile and Run Your First Java Program. The same general engineering habit appears elsewhere, but the evidence and failure signals in this First Program lesson are specific to this mechanism.

In Understand every file that appeared, look at Compile and Run Your First Java Program through the constraint that matters in this part of the lesson: make the relevant state visible before you change it, then compare the observed result with the contract you expected. In Java, this prevents a local-looking edit from hiding an environment, data, permission, lifecycle or runtime assumption. Record the evidence from this step because the next decision in the First Program module should be based on what you measured rather than on a repeated rule of thumb.

Run it and observe the actual result

In the First Program part of this learning path, Compile and Run Your First Java Program is deliberately introduced now because later lessons depend on the boundary it establishes. The learner should be able to describe the inputs, the operation, and the result in plain language. In the running scenario—build a small domain application that grows into tested Spring-backed services—the input might be a value, request, record, event, configuration setting, or user action. The operation is the part controlled by Compile and Run Your First Java Program; the result is the state you can inspect afterward. Keeping those three pieces explicit prevents the lesson from collapsing into memorized commands. In this lesson's Compile and Run Your First Java Program example, record the evidence you observed rather than treating the rule as a slogan; that note becomes useful when the next First Program exercise changes the conditions. In Java lesson 7 — Write Compile and Run Your First Java Program, use that observation as the checkpoint for this exact First Program topic rather than generalizing it beyond the evidence.

A production system rarely fails at the exact line shown in a beginner example, so this section connects Compile and Run Your First Java Program to the surrounding runtime and operational context. Documentation often presents the API or syntax first because reference pages are written for lookup. A tutorial has a different job. Here the explanation begins with intent, then shows the smallest concrete implementation, then adds constraints. That order lets you understand why a setting or line exists before you are asked to remember its spelling. The specific test here is about Compile and Run Your First Java Program: change one relevant input, configuration value or boundary and make sure the result still matches the contract described above.

Worked example: Compile and Run Your First Java Program

The following java example is written specifically for this lesson. Read the requirement first, then predict the important result before running or reproducing it.

import java.util.ArrayList;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        List<Integer> values = new ArrayList<>(List.of(12, 18, 25, 31));
        values.removeIf(value -> value < 20);
        System.out.println(values);
    }
}
``` In this lesson's **Compile and Run Your First Java Program** example, record the evidence you observed rather than treating the rule as a slogan; that note becomes useful when the next First Program exercise changes the conditions.

**Expected observation**

[25, 31]

### Read the example deliberately

- **Line/construct 1:** `import java.util.ArrayList;` — identify what state or contract this introduces, then trace where that state is consumed.
- **Line/construct 2:** `import java.util.List;` — identify what state or contract this introduces, then trace where that state is consumed.
- **Line/construct 3:** `public class Main {` — identify what state or contract this introduces, then trace where that state is consumed.
- **Line/construct 4:** `public static void main(String[] args) {` — identify what state or contract this introduces, then trace where that state is consumed.
- **Line/construct 5:** `List<Integer> values = new ArrayList<>(List.of(12, 18, 25, 31));` — identify what state or contract this introduces, then trace where that state is consumed.
- **Line/construct 6:** `values.removeIf(value -> value < 20);` — identify what state or contract this introduces, then trace where that state is consumed.
- **Line/construct 7:** `System.out.println(values);` — identify what state or contract this introduces, then trace where that state is consumed.
- **Line/construct 8:** `}` — identify what state or contract this introduces, then trace where that state is consumed.
- **Line/construct 9:** `}` — identify what state or contract this introduces, then trace where that state is consumed.

Do not stop at “it ran.” Change one meaningful value related to Compile and Run Your First Java Program, predict the new result, run/reproduce the example again, and explain why the output changed. That mutation test is a stronger check of understanding than copying the original result.

## Change one thing and predict the result

For a Java developer, Compile and Run Your First Java Program becomes useful when it changes a decision you can verify. The learner should be able to describe the inputs, the operation, and the result in plain language. In the running scenario—build a small domain application that grows into tested Spring-backed services—the input might be a value, request, record, event, configuration setting, or user action. The operation is the part controlled by Compile and Run Your First Java Program; the result is the state you can inspect afterward. Keeping those three pieces explicit prevents the lesson from collapsing into memorized commands. For **Compile and Run Your First Java Program**, apply this check in the context of the **First Program** workflow before carrying the assumption into later Java work.

For this part of **Write Compile and Run Your First Java Program**, move beyond the earlier mental model and ask how the behavior survives repetition. Run or reproduce the step twice, change the ordering or boundary case where safe, and verify that the same invariant still holds. A reliable First Program workflow is one that produces evidence you can compare, not one that succeeds only when the exact tutorial sequence is copied.

## Trace control and data through the example

For the **Trace control and data through the example** part of Write Compile and Run Your First Java Program, use a separate verification pass rather than repeating the earlier explanation. Focus on **Compile and Run Your First Java Program** under one changed condition and write down the before/after evidence. This is verification pass 2 for Java lesson 7: the useful outcome is a concrete observation—output, state, diagnostic, generated artifact, query result or test result—that another learner can reproduce in the First Program workflow.

There are usually several ways to accomplish the same visible result. The important skill is knowing which guarantees differ when you choose one form of Compile and Run Your First Java Program over another. Documentation often presents the API or syntax first because reference pages are written for lookup. A tutorial has a different job. Here the explanation begins with intent, then shows the smallest concrete implementation, then adds constraints. That order lets you understand why a setting or line exists before you are asked to remember its spelling. Keep this point tied to **Compile and Run Your First Java Program**. The same general engineering habit appears elsewhere, but the evidence and failure signals in this First Program lesson are specific to this mechanism.

### Failure-mode matrix

| Symptom | Likely category | First evidence to collect |
|---|---|---|
| The Compile and Run Your First Java Program behavior never occurs | configuration / control flow | verify the relevant code/configuration is actually reached |
| Build or validation fails | syntax / type / unsupported option | read the first meaningful diagnostic, not the last cascade message |
| Works locally but not elsewhere | environment / version / permission | compare runtime versions, identity, configuration and data |
| Result is valid but wrong | assumption / data shape / business rule | inspect intermediate values and boundary conditions |
| Intermittent behavior | concurrency / timing / external dependency | add timestamps, correlation IDs or deterministic reproduction |

## Turn the demo into a repeatable workflow

For the **Turn the demo into a repeatable workflow** part of Write Compile and Run Your First Java Program, use a separate verification pass rather than repeating the earlier explanation. Focus on **Compile and Run Your First Java Program** under one changed condition and write down the before/after evidence. This is verification pass 3 for Java lesson 7: the useful outcome is a concrete observation—output, state, diagnostic, generated artifact, query result or test result—that another learner can reproduce in the First Program workflow.

A production system rarely fails at the exact line shown in a beginner example, so this section connects Compile and Run Your First Java Program to the surrounding runtime and operational context. Documentation often presents the API or syntax first because reference pages are written for lookup. A tutorial has a different job. Here the explanation begins with intent, then shows the smallest concrete implementation, then adds constraints. That order lets you understand why a setting or line exists before you are asked to remember its spelling. In this lesson's **Compile and Run Your First Java Program** example, record the evidence you observed rather than treating the rule as a slogan; that note becomes useful when the next First Program exercise changes the conditions.

## What breaks first and why

Now apply **Compile and Run Your First Java Program** to the current **What breaks first and why** concern. Start from the smallest state that demonstrates the behavior, vary one input or configuration choice, and explain the result in terms of the Java runtime or platform. If two outcomes look similar in the UI, use logs, return values, generated artifacts, query results, tests or another concrete signal to distinguish them.

This section needs a different question from the earlier explanation: what would make **Compile and Run Your First Java Program** fail specifically while working through **What breaks first and why**? Choose one realistic boundary, reproduce it deliberately, and inspect the first useful diagnostic or intermediate value. The aim in Write Compile and Run Your First Java Program is to recognize the mechanism under changed conditions, not to repeat the same successful path with different wording.

## Debugging the first failure

Before adding more syntax, make the state of the system observable. That habit matters especially when working with Compile and Run Your First Java Program. The learner should be able to describe the inputs, the operation, and the result in plain language. In the running scenario—build a small domain application that grows into tested Spring-backed services—the input might be a value, request, record, event, configuration setting, or user action. The operation is the part controlled by Compile and Run Your First Java Program; the result is the state you can inspect afterward. Keeping those three pieces explicit prevents the lesson from collapsing into memorized commands. In this lesson's **Compile and Run Your First Java Program** example, record the evidence you observed rather than treating the rule as a slogan; that note becomes useful when the next First Program exercise changes the conditions.

This section needs a different question from the earlier explanation: what would make **Compile and Run Your First Java Program** fail specifically while working through **Debugging the first failure**? Choose one realistic boundary, reproduce it deliberately, and inspect the first useful diagnostic or intermediate value. The aim in Write Compile and Run Your First Java Program is to recognize the mechanism under changed conditions, not to repeat the same successful path with different wording.

## Clean up the example without hiding the fundamentals

In the First Program part of this learning path, Compile and Run Your First Java Program is deliberately introduced now because later lessons depend on the boundary it establishes. The learner should be able to describe the inputs, the operation, and the result in plain language. In the running scenario—build a small domain application that grows into tested Spring-backed services—the input might be a value, request, record, event, configuration setting, or user action. The operation is the part controlled by Compile and Run Your First Java Program; the result is the state you can inspect afterward. Keeping those three pieces explicit prevents the lesson from collapsing into memorized commands. The specific test here is about **Compile and Run Your First Java Program**: change one relevant input, configuration value or boundary and make sure the result still matches the contract described above.

A production system rarely fails at the exact line shown in a beginner example, so this section connects Compile and Run Your First Java Program to the surrounding runtime and operational context. Documentation often presents the API or syntax first because reference pages are written for lookup. A tutorial has a different job. Here the explanation begins with intent, then shows the smallest concrete implementation, then adds constraints. That order lets you understand why a setting or line exists before you are asked to remember its spelling. Keep this point tied to **Compile and Run Your First Java Program**. The same general engineering habit appears elsewhere, but the evidence and failure signals in this First Program lesson are specific to this mechanism.

## A slightly more realistic variation

In **A slightly more realistic variation**, look at **Compile and Run Your First Java Program** through the constraint that matters in this part of the lesson: make the relevant state visible before you change it, then compare the observed result with the contract you expected. In Java, this prevents a local-looking edit from hiding an environment, data, permission, lifecycle or runtime assumption. Record the evidence from this step because the next decision in the First Program module should be based on what you measured rather than on a repeated rule of thumb.

For the **A slightly more realistic variation** part of Write Compile and Run Your First Java Program, use a separate verification pass rather than repeating the earlier explanation. Focus on **Compile and Run Your First Java Program** under one changed condition and write down the before/after evidence. This is verification pass 2 for Java lesson 7: the useful outcome is a concrete observation—output, state, diagnostic, generated artifact, query result or test result—that another learner can reproduce in the First Program workflow.

## A production-oriented walkthrough for Compile and Run Your First Java Program

### 1. Establish the Compile and Run Your First Java Program behavior

Establish this step in the context of build a small domain application that grows into tested Spring-backed services. Keep the change small enough that you can state the expected result before executing it. Capture the relevant input, configuration or code, then record the observable result. If the result differs from the prediction, do not add more changes yet; narrow the mismatch using diagnostics appropriate to a modern JDK, IntelliJ/VS Code and build tooling. For **Compile and Run Your First Java Program**, apply this check in the context of the **First Program** workflow before carrying the assumption into later Java work.

### 2. Inspect the Compile and Run Your First Java Program behavior

Inspect this step in the context of build a small domain application that grows into tested Spring-backed services. Keep the change small enough that you can state the expected result before executing it. Capture the relevant input, configuration or code, then record the observable result. If the result differs from the prediction, do not add more changes yet; narrow the mismatch using diagnostics appropriate to a modern JDK, IntelliJ/VS Code and build tooling. The specific test here is about **Compile and Run Your First Java Program**: change one relevant input, configuration value or boundary and make sure the result still matches the contract described above.

### 3. Implement the Compile and Run Your First Java Program behavior

Implement this step in the context of build a small domain application that grows into tested Spring-backed services. Keep the change small enough that you can state the expected result before executing it. Capture the relevant input, configuration or code, then record the observable result. If the result differs from the prediction, do not add more changes yet; narrow the mismatch using diagnostics appropriate to a modern JDK, IntelliJ/VS Code and build tooling. The specific test here is about **Compile and Run Your First Java Program**: change one relevant input, configuration value or boundary and make sure the result still matches the contract described above.

A useful variation is to introduce one boundary case that is plausible for Compile and Run Your First Java Program: an empty value, a missing permission, an unexpected type, a repeated operation, an unavailable dependency, or a larger-than-normal input. The exact case depends on the technology, but the reasoning is the same—state the invariant you expect to remain true, then verify it explicitly. Keep this point tied to **Compile and Run Your First Java Program**. The same general engineering habit appears elsewhere, but the evidence and failure signals in this First Program lesson are specific to this mechanism. In **Java lesson 7 — Write Compile and Run Your First Java Program**, use that observation as the checkpoint for this exact First Program topic rather than generalizing it beyond the evidence.

### 4. Exercise the Compile and Run Your First Java Program behavior

Exercise this step in the context of build a small domain application that grows into tested Spring-backed services. Keep the change small enough that you can state the expected result before executing it. Capture the relevant input, configuration or code, then record the observable result. If the result differs from the prediction, do not add more changes yet; narrow the mismatch using diagnostics appropriate to a modern JDK, IntelliJ/VS Code and build tooling. For **Compile and Run Your First Java Program**, apply this check in the context of the **First Program** workflow before carrying the assumption into later Java work.

### 5. Challenge the Compile and Run Your First Java Program behavior

Challenge this step in the context of build a small domain application that grows into tested Spring-backed services. Keep the change small enough that you can state the expected result before executing it. Capture the relevant input, configuration or code, then record the observable result. If the result differs from the prediction, do not add more changes yet; narrow the mismatch using diagnostics appropriate to a modern JDK, IntelliJ/VS Code and build tooling. In this lesson's **Compile and Run Your First Java Program** example, record the evidence you observed rather than treating the rule as a slogan; that note becomes useful when the next First Program exercise changes the conditions.

A useful variation is to introduce one boundary case that is plausible for Compile and Run Your First Java Program: an empty value, a missing permission, an unexpected type, a repeated operation, an unavailable dependency, or a larger-than-normal input. The exact case depends on the technology, but the reasoning is the same—state the invariant you expect to remain true, then verify it explicitly. In this lesson's **Compile and Run Your First Java Program** example, record the evidence you observed rather than treating the rule as a slogan; that note becomes useful when the next First Program exercise changes the conditions.

### 6. Verify the Compile and Run Your First Java Program behavior

Verify this step in the context of build a small domain application that grows into tested Spring-backed services. Keep the change small enough that you can state the expected result before executing it. Capture the relevant input, configuration or code, then record the observable result. If the result differs from the prediction, do not add more changes yet; narrow the mismatch using diagnostics appropriate to a modern JDK, IntelliJ/VS Code and build tooling. In this lesson's **Compile and Run Your First Java Program** example, record the evidence you observed rather than treating the rule as a slogan; that note becomes useful when the next First Program exercise changes the conditions.

### 7. Harden the Compile and Run Your First Java Program behavior

Harden this step in the context of build a small domain application that grows into tested Spring-backed services. Keep the change small enough that you can state the expected result before executing it. Capture the relevant input, configuration or code, then record the observable result. If the result differs from the prediction, do not add more changes yet; narrow the mismatch using diagnostics appropriate to a modern JDK, IntelliJ/VS Code and build tooling. For **Compile and Run Your First Java Program**, apply this check in the context of the **First Program** workflow before carrying the assumption into later Java work.

For the **A production-oriented walkthrough for Compile and Run Your First Java Program** part of Write Compile and Run Your First Java Program, use a separate verification pass rather than repeating the earlier explanation. Focus on **Compile and Run Your First Java Program** under one changed condition and write down the before/after evidence. This is verification pass 4 for Java lesson 7: the useful outcome is a concrete observation—output, state, diagnostic, generated artifact, query result or test result—that another learner can reproduce in the First Program workflow.

### 8. Document the Compile and Run Your First Java Program behavior

Document this step in the context of build a small domain application that grows into tested Spring-backed services. Keep the change small enough that you can state the expected result before executing it. Capture the relevant input, configuration or code, then record the observable result. If the result differs from the prediction, do not add more changes yet; narrow the mismatch using diagnostics appropriate to a modern JDK, IntelliJ/VS Code and build tooling. In this lesson's **Compile and Run Your First Java Program** example, record the evidence you observed rather than treating the rule as a slogan; that note becomes useful when the next First Program exercise changes the conditions.

## Where Compile and Run Your First Java Program implementations commonly go wrong

### Treating Compile and Run Your First Java Program as syntax instead of behavior
If you can reproduce the syntax but cannot predict the state after it runs, the lesson is not finished. Rewrite the example in your own words and name the input, operation and observable result.

### Copying a configuration from a different version
Java tooling evolves. Compare the documentation version, runtime/tool version and project settings before assuming that a screenshot or command from another environment applies unchanged.

### Verifying only the happy path
A successful first run proves one path. Add at least one negative or boundary case relevant to Compile and Run Your First Java Program. The failure should be intentional and the diagnostic should make sense.

### Hiding the important state behind too much abstraction
Abstraction is useful after the behavior is understood. During the first implementation of Compile and Run Your First Java Program, keep the decisive state and control flow visible enough to debug.

## Diagnosing Compile and Run Your First Java Program systematically

Use this order when Compile and Run Your First Java Program does not behave as expected:

1. Reproduce the smallest failing case.
2. Confirm the actual version/toolchain/environment.
3. Capture the first meaningful diagnostic or unexpected value.
4. Verify identity, permissions and configuration if the operation crosses a service boundary.
5. Inspect intermediate state rather than only the final UI.
6. Change one variable and rerun.
7. Compare the corrected behavior with a negative case.
8. Record the final cause so the same failure is faster to diagnose next time.

## Practice: change the constraint

Extend the worked scenario so that **Compile and Run Your First Java Program** must handle one additional real constraint. Choose one: a second data shape, a failed dependency, an invalid input, a permission difference, a repeat operation, or a larger workload. Before implementing the change, write down the behavior you expect and the evidence that will prove it.

Your result is complete when another learner can reproduce the change from your notes, observe the expected behavior, and intentionally trigger at least one documented failure without damaging their environment. In this lesson's **Compile and Run Your First Java Program** example, record the evidence you observed rather than treating the rule as a slogan; that note becomes useful when the next First Program exercise changes the conditions.

## Before you move on

- Can you define **Compile and Run Your First Java Program** without using the exact wording of an API/reference page?
- Can you identify the boundary where Compile and Run Your First Java Program begins and where another concept takes over?
- Can you predict the result of the worked example before running it?
- Can you explain one failure from evidence rather than guessing?
- Can you name one production constraint that the beginner example intentionally simplifies?
- Can you repeat the example from a clean state?

## Keep these Compile and Run Your First Java Program principles

- **Compile and Run Your First Java Program** is useful because it controls observable behavior, not because it adds another piece of syntax to memorize.
- Verification belongs in the workflow: build/check, run/reproduce, inspect, challenge, and repeat.
- The First Program module uses this lesson as a foundation for the next decisions in the Java learning path.
- Official documentation is the source of truth for version-specific contracts; tutorials should teach you how to read and apply those contracts.

## Documentation to keep beside this lesson

The following primary documentation was used as a factual reference map for this lesson. ScrutnLearn's explanation is original synthesis rather than copied documentation prose.

- [Dev.java Learn](https://dev.java/learn/)
- [Java SE API documentation](https://docs.oracle.com/en/java/javase/)
- [JDBC tutorial](https://docs.oracle.com/javase/tutorial/jdbc/)
- [Maven guides](https://maven.apache.org/guides/)
- [OpenJDK](https://openjdk.org/)