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Java CheatSheet

Modern Java is a strongly-typed, eagery evaluated, case sensative, yet whitespace insensative language. It uses hierarchies of classes/types to structure data, but also has first-class support for functional-style algebraic datatypes.

Java programs are made up of ‘classes’, classes contain methods, and methods contain commands. To just try out a snippet of code, we can

• Open a terminal and enter jshell; then enter:

  1 + 2 // The jshell lets you try things out!
  
  // Say hello in a fancy way
  import javax.swing.*;
  JOptionPane.showMessageDialog(new JFrame(), "Hello, World!");
  
  

• Alternatively, in IntelliJ, click Tools then Groovy Console to try things out!
• Finally, VSCode allows arbitrary Java code to be sent to a jshell in the background(!) and it echoes the result in a friendly way.

In order to run a java program, it must have a main method as an entry point.

public class LearnJava {
    // In order to run a java program, it must have a main method as an entry
    // point.
    public static void main(String[] args) {
        System.out.println("Hello World!");

        // Use System.out.printf() for easy formatted printing.
        System.out.printf("pi = %.5f", Math.PI); // => pi = 3.14159
    }
}

Arabic CheatSheet

Life & Computing Science by Musa Al-hassy is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License