Synchronization in compiling

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Synchronous in method

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int i;
synchronized int fun() {
	return ++i;
}

javap

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synchronized int fun();
    Code:
       0: aload_0
       1: dup
       // Field i:I
       2: getfield      #2
       5: iconst_1
       6: iadd
       7: dup_x1
       // Field i:I
       8: putfield      #2
      11: ireturn

synchronized method is simply distinguished
in the run-time constant pool by the ACC_SYNCHRONIZED flag

Synchronous in block

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int i;
void fun(Object obj, int j) {
	synchronized(obj) {
		i+=j;
	}
}

javap

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void fun(java.lang.Object, int);
    Code:
       0: aload_1
       1: dup
       2: astore_3
       3: monitorenter
       4: aload_0
       5: dup
       // Field i:I
       6: getfield      #2                  
       9: iload_2
      10: iadd
      // Field i:I
      11: putfield      #2
      14: aload_3
      15: monitorexit
      16: goto          26
      19: astore        4
      21: aload_3
      22: monitorexit
      23: aload         4
      25: athrow
      26: return
    Exception table:
       from    to  target type
           4    16    19   any
          19    23    19   any

monitorexit will be executed definitely
If not exit normally, #25 will throw exception