Static blocks in Java

Unlike C++, Java supports a special block, called static block (also called static clause) which can be used for static initializations of a class. This code inside static block is executed only once: the first time the class is loaded into memory. For example, check output of following Java program.

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// filename: Main.java
class Test {
    static int i;
    int j;
      
    // start of static block 
    static {
        i = 10;
        System.out.println("static block called ");
    }
    // end of static block 
}
  
class Main {
    public static void main(String args[]) {
  
        // Although we don't have an object of Test, static block is 
        // called because i is being accessed in following statement.
        System.out.println(Test.i); 
    }
}

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Output:

static block called

10





Also, static blocks are executed before constructors. For example, check output of following Java program.











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// filename: Main.java 


class Test { 


    static int i; 


    int j; 


    static { 


        i = 10; 


        System.out.println("static block called "); 


    } 


    Test(){ 


        System.out.println("Constructor called"); 


    } 


} 


  


class Main { 


    public static void main(String args[]) { 


  


       // Although we have two objects, static block is executed only once. 


       Test t1 = new Test(); 


       Test t2 = new Test(); 


    } 


} 



















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Output:

static block called

Constructor called

Constructor called




What if we want to execute some code for every object?

We use Initializer Block in Java




References:

Thinking in Java Book


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