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1.12 Variables

Variables, whether local or global, can be declared and initialized in several ways:
  • To declare: int i;
  • To declare and initialize: int i = 10;
  • To initialize after declaration: i = 20;
  • To declare multiple: int i, j, k;
  • To declare and initialize multiple: int i = 0, j = 9, k = -2;
  • To initialize multiple after declaration: i = j = k = -1;

Like methods, variables can have specifiers to denote their access levels:

  • private int i;
  • int j;
  • protected int k;
  • public int l;
  • The access level specifier is summarized in the following table:

    Specifier Class Package Subclass World  
    private Yes No No No This variable can only be read and modified from within the same class. If at all, the value is accessed by a method (e.g. getValue()) and modified through some other method that presumably involves checking the data.
    no specifier (blank) Yes Yes No No This variable can additionally be read and modified by other classes in the package.
    protected Yes Yes Yes No This variable can additionally be read and modified by classes that have been derived from this class.
    public Yes Yes Yes Yes This variable can be read and modified by any class from anywhere.

Local variables can be declared at any point, whether in the beginning of a method, or anywhere else. This is somewhat different from C, where variables must be declared at the beginning of a function.

public void computeSomething(int a) {

  int i = 0;
  ...
  // lots of code
  ...
  String s = "This is towards the end";
  ...
  ...
}
Global variables must be declared within the class, but outside of any method:

public class MyClass {

  int age;
  String firstName;

  public MyClass {

    ...
  }

  ...
}