Java Tutorial/Language/Variables

Demonstrate lifetime of a variable

public class MainClass {
  public static void main(String args[]) {
    int x;
    for (x = 0; x < 3; x++) {
      int y = -1; // y is initialized each time block is entered
      System.out.println("y is: " + y); // this always prints -1
      y = 100;
      System.out.println("y is now: " + y);
    }
  }
}

y is: -1
y is now: 100
y is: -1
y is now: 100
y is: -1
y is now: 100

helloMessage variable is declared as a local variable:

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

shows the proper way to declare a class variable named helloMessage

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

Variable Dynamic Initialization

public class MainClass {
  public static void main(String args[]) {
    double a = 3.0, b = 4.0;
    // c is dynamically initialized
    double c = Math.sqrt(a * a + b * b);
    System.out.println("Hypotenuse is " + c);
  }
}

Hypotenuse is 5.0

Variables

Variables are data placeholders. There are two data types in Java:

1. Reference types provides a reference to an object.
2. Primitive types hold a primitive.

You don"t have to place class variable declarations at the beginning of a class.

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