Does the 'java' Command Compile Java Programs?

Does the 'java' command also compile Java programs, or is that solely the job of 'javac'? Why do we need both commands?

public class Myclass {
 public static void main(String[] args){
    System.out.println("hello world");
  }
}

In Java, the 'javac' command is specifically designed to compile Java source files into bytecode (.class files), while the 'java' command is used to run those compiled bytecode files. This distinction is crucial to understand for proper Java programming and execution.

// Compile the code
$ javac Myclass.java

// Run the compiled bytecode
$ java Myclass

Causes

• The 'javac' command compiles Java source files (.java) into bytecode (.class) which can be executed by the Java Virtual Machine (JVM).
• The 'java' command interprets and runs the compiled bytecode files, not the source code directly.

Solutions

• Always compile your Java programs using the 'javac' command before executing them with 'java'.
• Ensure the file name matches the public class name to avoid compilation errors.

Mistake: Running a Java source file directly using the 'java' command.

Solution: Use 'javac' to compile the source file first, then use 'java' to run the compiled class.

Mistake: Not matching the public class name with the filename.

Solution: Ensure the filename matches the public class name (e.g., Myclass.java for public class Myclass).