Tag: programming

What kind of bytecode does the Java compiler generate for a static initializer block?

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As it turns out the compiler generates a second static constructor besides the default constructor. Look at the class and corresponding bytecode below:

/**
 *
 */
public class ClassWithStaticBlock {
    static int i;
    
    static {
        i = 2;
    }
}

You can lookup the bytecode mnemonics here.

// class version 49.0 (49)
// access flags 0x21
public class ClassWithStaticBlock {

  // compiled from: ClassWithStaticBlock.java

  // access flags 0x8
  static I i

  // access flags 0x1
  // generated default constructor
  public ()V
   L0
    LINENUMBER 4 L0
    ALOAD 0
    INVOKESPECIAL java/lang/Object. ()V
    RETURN
   L1
    LOCALVARIABLE this LClassWithStaticBlock; L0 L1 0
    MAXSTACK = 1
    MAXLOCALS = 1

  // access flags 0x8
  // static constuctor
  static ()V
   L0
    LINENUMBER 8 L0
    ICONST_2 // push int value 2 on the operand stack
    PUTSTATIC ClassWithStaticBlock.i : I // pop value off the stack and assign it to the static field
   L1
    LINENUMBER 9 L1
    RETURN
    MAXSTACK = 1
    MAXLOCALS = 0
}