Java Environment Setup
In this page:
What is the JDK?
The JDK bundles everything you need to build Java software: the javac compiler, the java launcher, debugging tools, and the JRE (which itself contains the JVM and core class libraries) needed just to run compiled programs.
Example: What is the JDK?
public class Main {
// The JDK provides: javac (compiler), java (launcher), debugging tools, and the JRE/JVM
public static void main(String[] args) {
System.out.println("Built and run using tools bundled in the JDK.");
}
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Writing Your Code
Any plain text editor works, but IDEs like IntelliJ IDEA, Eclipse, or VS Code with the Java extension pack add real value here -- autocomplete, inline error highlighting, and one-click running that make catching typos far faster.
Example: Writing Your Code
public class Main {
// Written in an IDE like IntelliJ IDEA, Eclipse, or VS Code (Java extension pack)
public static void main(String[] args) {
System.out.println("Code written with autocomplete and inline error highlighting.");
}
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Saving Your File
Java is strict about this: if your file declares public class Calculator, it must be saved as Calculator.java exactly, matching case, or the compiler will refuse to build it.
Example: Saving Your File
public class Calculator {
// This file MUST be saved as Calculator.java, matching the class name exactly (case-sensitive)
public static void main(String[] args) {
System.out.println("Saved as Calculator.java to match 'public class Calculator'.");
}
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Compiling Your Code
Running javac filename.java from your terminal reads your source, checks it for syntax and type errors, and if it's clean, emits a matching filename.class file containing JVM bytecode in the same folder.
Example: Compiling Your Code
public class Main {
// Terminal: javac Main.java
// Checks syntax/types, then emits Main.class (JVM bytecode) in the same folder
public static void main(String[] args) {
System.out.println("Compiled with: javac Main.java");
}
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Running the Bytecode
The java ClassName command (note: no .java or .class extension here) loads that bytecode file and hands it to the JVM, which begins executing from your program's main method.
Example: Running the Bytecode
public class Main {
// Terminal: java Main (no .java or .class extension)
public static void main(String[] args) {
System.out.println("Executed by the JVM starting from main().");
}
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