Chapter01

Chapter 1: Getting Started: Compiling and Running Java

1.1 Compiling and Running Java: Standard JDK

Problem

You need to compile and run your Java program.

Solution

# compile the java class (HelloWorld.java)
javac HelloWorld.java

# run the compiled java class (HelloWorld.class)
java HelloWorld

Hellow World!

From Java 11 you can directly do

java HelloWorld.java

Hello, World!

To specify the output directory (for the .class file), -d can be used. i.e:

javac HelloWorld.java -d out/

1.3 Compiling, Running, and Testing with an IDE

Problem

It is cumbersome to use several tools for the various development tasks.

Solution

Use an Integrated Development Environment (IDE), which combines editing, testing, compiling, running, debugging, and package management.

1.4 Exploring Java with JShell

Problem

You want to try out Java expressions and APIs quickly, without having to create a file with

public class X {
  public static void main(String[] args) {
    // …
  }
}

every time.

Solution

Use JShell, Java’s REPL (Read-Evaluate-Print-Loop) interpreter.

Starting with Java 11, JShell is included as a standard part of Java

1.5 Using CLASSPATH Effectively

Problem

You need to keep your class files in a common directory, or you’re wrestling with CLASSPATH.

Solution

Set CLASSPATH to the list of directories and/or JAR files that contain the classes you want.

1.12 Getting Readable Stack Traces

Problem

You’re getting an exception stack trace at runtime, but most of the important parts don’t have line numbers.

Solution

Be sure you have compiled with debugging enabled.