Summary  
This chapter introduces how to structure a simple program with a main function, compile it, and use printing to display output.

General domain of usage  
Programming education and tutorials

package com.example;

import static org.junit.jupiter.api.Assertions.assertTrue;

import java.io.ByteArrayOutputStream;
import java.io.PrintStream;
import java.util.regex.Pattern;
import java.util.regex.Matcher;

import org.junit.jupiter.api.DisplayName;
import org.junit.jupiter.api.Test;

public class MainTest {

    @Test
    @DisplayName("main() prints Hello World!")
    void testPrintsHelloWorldFlexible() {
        ByteArrayOutputStream outContent = new ByteArrayOutputStream();
        PrintStream originalOut = System.out;
        System.setOut(new PrintStream(outContent));

        Main.main(new String[]{});

        System.setOut(originalOut);

        String output = outContent.toString().trim();

        Pattern pattern = Pattern.compile("hello\\\s+world\\\s*!?", Pattern.CASE_INSENSITIVE);
        assertTrue(pattern.matcher(output).find(), "Actual output: " + output);
    }
}

MainTest.java

A streamlined beginner module focused on the essential Java programming concepts: syntax, variables, data types, control flow, loops, arrays, and strings.

Your First Program

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