Static Methods in Java

A static method in a class is a method declared with the static modifier. The following is a class Helper defined with static methods abs() and main():

public class Helper
{
  public static int abs(int num)
  {
    return (num < 0) ? (-num) : num;
  }
  public static void main(String[]args)
  {
    System.out.println(abs(5));
  }
}

The signature of the method abs() is:

  public static int abs(int num)

It has the following parts:

  • public: access modifier, which indicates the method is accessible outside of this class.
  • static: modifier, which indicates this is a static method.
  • int: the type of the return value. The return type could be void, which means no returns.
  • abs: the method name
  • (int num): the parameter list. Here there is only one parameter num of type int.

The method body is enclosed with brackets {}; it contains the code to be executed when the method is called. If the return type is not void, we have to have a return statement in every branch of control flow.

The main() method is also a static method, with no returns but with an array of strings as the parameter.

Static methods can not directly call a non-static method within the same class, since a non-static method needs instantiating an object. To access a static method in another class, we can directly use the class name followed by the method name. For example,

  Helper.abs(-3);

Static methods are often used in code libraries. For example,

Integer.parseInt("123");     // Convert string to integer
Double.parseDouble("1.23");  // Convert string to double
Math.sqrt(123);              // Compute the square root
Math.random();               // Generate a random number

Related documents:
http://docs.oracle.com/javase/7/docs/api/java/lang/Integer.html#parseInt(java.lang.String)
http://docs.oracle.com/javase/7/docs/api/java/lang/Double.html#parseDouble(java.lang.String)
http://docs.oracle.com/javase/7/docs/api/java/lang/Math.html

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