Java Cheat-sheet

Overview

This cheat-sheet is for those who have a general understanding of programming. Keep this open while you code for easy Java-programming.

• Key Notes
• Java Class
• Objects & Imports
• Support
• Licence

Key Notes

• All lines end in semicolons.
• Varaibles and functions must have a declared type. The different types are:
  • boolean: a variable that is always either true or false.
  • int: a number that is not a decimal (Ex. 1, 0, -1)
  • String: text (Ex. "hello")
  • char: a single character (Ex. 'A')
  • float: a number that can be a decimal (Ex. -1.0, 7.2)
  • double: a number that can be a decimal (stores twice as many digits as float)
• Before the variable or function type, you may indicate if the variable is private or public.
• Functions and variables can also be indicated to be static (able to be accessed by other functions).
• Functions must have a return statement that returns a variable of the function type.
  • int myFunction() {return 5;}
• Functions that don't return a value are of type void.
  • void myFunction() {System.out.println("Hello World!");}

Java Class

Java files end in .java. All java files must have a class. The class name must be the name of the file (with the .java omitted). When the class is run, the main function is run. Example:

public class Main {
    public static void main(String[] args) {
        System.out.println("Hello World!");
    }
}

Objects & Imports

You can create an object by using a constructor. Example:

package folder;

public class Object {
    public Object() {}
}

import Object.java;

public class Main {
    Object a = new Object();
}

Note: Main and Object are in two different files and in the same folder ("folder"). The line public Object() {} is a constructor. Constructors return no type.

Support

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Licence

MIT © Timothy Lin