Java Programming Overview

Overview and Basics

by D1J1T — in Java — Updated: Feb 12, 2015 at 11:55 am

The goal of this article is to provide an introduction to the basics of programming in Java. It is written with no assumptions of prior programming experience and in a sense meant as a "crash course" to enable quick learning.

Let's Not Waste Time

Still Here?

Test Your Environment

  public class HelloWorld {

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

  }

public Who? static What?

Java Variable Types

  var myNum = 3;
  var myChar = 'c';

  int myNum = 3;
  char myChar = 'c';

Variable Declaration and Initialization

  int myNum; //declared, but not initialized. if this variable is accessed in the program, a null pointer exception will be thrown
  int alsoMyNum = 3; //declared and initialized as all of the others below.
  int yetAnotherNum = 7;
  float numWithPoint = 0.3;
  char myLetter = 'd';
  boolean mySwitch = true;
  DJSCustomClass djscc = new DJSCustomClass("strArg1",7,false);

I Like Cats!

  public class Animal {
  
  }

  public class Animal {
    int numLegs;
	boolean isHungry;
    String soundMade;
	public void makeNoise() {
	  playSound(soundMade);
	}
  }

  public class Cat extends Animal {
    
  }

  public class Cat extends Animal {
    public Cat() {
	  numLegs=4;
	  isHungry=true;
	  soundMade="Meow";
	  makeNoise(soundMade);
	}
  }

And Now, More Syntax

So Now I Know Where to Put My ; !!!

import java.awt.*;
import java.applet.Applet;
import java.coolPackage.CoolerClass;

  public class Cat extends Animal {
   ...
  }

• This one you should know already. If you don't know something specific, Google it. Getting a unique error? I'd bet it's not very unique. More than likely, someone else has had that problem. You'll find Stack Overflow. to be an excellent source. It's answered hundreds of my questions.
• Take online tutorials. A lot of them. They're free!!!
• Again, reference the Java docs often.
• Learn camel-case. It's simple. I should've explained it already, but here it is. class names start with an upper case letter. Everything else starts with a lower case letter. With variables and methods, they start with lower case, then every word contained within is capitalized. For example: myFirstVariable OR myFirstMethod();
• Print out your variables to your log or console at least. If you don't know the value of one, make sure you can see it. This applies to colors as well for example. If you need to see the color of a square, write helper code to do so.
• Re-compile often and test, test, test... Every case you can think of. Your users will think of others.
• Plan you're project out well. This will save you time. I promise. It is painful to spend days on a project only to realize that you should've used other structures.
• Variables are for the program/object state and there are 8 primitive types and unlimited class types.
• Methods define the program or object's behavior.
• Classes are a template for an object.
• Packages are libraries of classes that are related.
• In the example above, the makeNoise method is defined in the Animal class, but is called (executed) in the Cat class.
• Java uses common operators: +, -, *, / for math. Also % (modulus) will return the remainder. ++ will increment, -- will decrement.
• Logical operators include && (AND), || (OR), ! (NOT)
• Don't confuse = (assignment) with == (comparison)
• Conditionals/comparisons are used in if, if...else, while, do...while, for, switch

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If you find these articles to be helpful, I could always use another cup of coffee! Social media likes/+1s are also much appreciated. Thanks for reading!