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 you make an object of that class or the first time you access a static member of that class (even if you never make an object of that class). For example, check output of following Java program.

// 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);  
    } 
} 

Output:
static block called
10

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

// 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(); 
    } 
} 

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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