The use of Java static keyword

Java static keyword uses

The primary use of static keyword in java is memory management.Static keyword can  be used in

• Variables

• Methods

• blocks

• nested  classes.

1.Java static variable

Java static variable gets memory once.This means that the value once assigned does not change.Static variable can be used only to refer a common property with class objects.

Example.

/**
 *
 * @author Eric
 * Blog:www.techoverload.net
 */
public class StudentClass {
    int id;
    String name;
    static String className="BIT2016";
    
    StudentClass(int idNo,String n)
    {
    id=idNo;
    name=n;
    }
    
    void showDetails()
    {
      System.out.println("=========Student Details======");
    System.out.println("Student ID "+id);
      System.out.println("Student Name "+name);
        System.out.println("Student Class"+className);
      System.out.println("===============================");
    }
    public static void main(String args[])
    {
    StudentClass c=new StudentClass(1112,"Eric");
      StudentClass c2=new StudentClass(1113,"Jane");
      c.showDetails();
      c2.showDetails();
    }
}

Counter program without static variable

Below code demonstrate how we loose the value of counter variable because it has not been declared static.This is because the variable get assigned a value each time a new object is created.

Example

/**
 *
 * @author Eric
 * Blog:www.techoverload.net
 */
public class CounterClass {
    int count=0;
    CounterClass()
    {
    count++;
    
    System.out.println("The count is " +count);
    }
    public static void main(String args[])
    {
    CounterClass c=new CounterClass();
       CounterClass c2=new CounterClass();
          CounterClass c3=new CounterClass();
    
    }
    
}

Output

The count is 1

The count is 1

The count is 1

Counter program with static variable

/**
 *
 * @author Eric
 * Blog:www.techoverload.net
 */
public class CounterClass {
    static int count=0;
    CounterClass()
    {
    count++;
    
    System.out.println("The count is " +count);
    }
    public static void main(String args[])
    {
    CounterClass c=new CounterClass();
       CounterClass c2=new CounterClass();
          CounterClass c3=new CounterClass();
    
    }
    
}

Output:

The count is 1

The count is 2

The count is 3

2.Java static method

If static keyword is used with any method,it becomes a static method.

Static method xstics

• static method belongs to the class and not the object.
• static method can be called without creating class instance.
• static method can access static data and change them.

Example

Below code shows a static method that has access to static variable and changes it.

/**
 *
 * @author Eric
 * Blog:www.techoverload.net
 */
public class StudentClass {
    int id;
    String name;
    static String className="BIT2016";
    
    StudentClass(int idNo,String n)
    {
    id=idNo;
    name=n;
    }
    
    static void changeClass()
    {
    className="BIT2017";
    }
    
    void showDetails()
    {
      System.out.println("=========Student Details======");
    System.out.println("Student ID "+id);
      System.out.println("Student Name "+name);
        System.out.println("Student Class"+className);
      System.out.println("===============================");
    }
    public static void main(String args[])
    {
    StudentClass c=new StudentClass(1112,"Eric");
    //calling static method
      StudentClass.changeClass();
      StudentClass c2=new StudentClass(1113,"Jane");
      c.showDetails();
      c2.showDetails();
      
    }
}

Example of static method to do calculations

/**
 *
 * @author Eric
 * Blog:www.techoverload.net
 */
public class Calculation {
    static int calc(int p)
    {
        return p*p*p;
    }
    public static void main(String args[])
    {
    int rs=Calculation.calc(20);
    System.out.println("The result is "+rs);
    }
    
}

Note that

• static method cannot use non static data member or call non static method.
• this and super cannot be used in static context.

3.Java static block

The main use  of static block is :-

Initialize static data member.
Executed before main method.

public class A2{  
  static{System.out.println("static block is invoked");}  
  public static void main(String args[]){  
   System.out.println("Hello main");  
  }  
}

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