Initialization block within a constructor

Question

I know that an initialization block runs after the call to 'super()' in a constructor. However, when looking through some code this morning, I found the following:

public class SimpleListLocalsAnalysis extends BackwardFlowAnalysis
    FlowSet emptySet;

    public SimpleLiveLocalsAnalysis(UnitGraph graph) {
        super(graph);

        {
            Chain locals = g.getBody().getLocals();
            FlowUniverse localUniverse = new FlowUniverse(locals.toArray());
            emptySet = new ArrayPackedSet(localUniverse);
        }

        doAnalysis();
    }
...
}

The above code shows some initialisation going on within an initialisation block just after 'super(graph)' invocation. What's the purpose of placing the code in an initialisation block within a constructor, as surely it runs anyway after the call to super. Am I missing something here?

Jigar Joshi · Accepted Answer · 2011-07-08 10:43:46Z

6

Its not initilization block, its simple block

just like

public void foo(){

  {
      //some code
  }
}

Purpose:

You can have restricted scope

answered Jul 8, 2011 at 10:43

Jigar Joshi

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4 Comments

Joeblackdev Over a year ago

So what's the purpose of a 'simple block'? Why use it?

Jigar Joshi Over a year ago

You can have advantage of scope.. you can do some local stuff in this block.

Joeblackdev Over a year ago

Ok, to ensure that whatever you define is not accessible outside of the block? Is this why you would use them?

Joeblackdev Over a year ago

Makes sense. I've never seen them before strangely enough. Thanks for the clarification.

Alvin · Accepted Answer · 2011-07-08 11:07:10Z

The best way to find out is probably to ask the author of the code. Maybe he surrounded the block of code to indicate the importance of those initialization. Or maybe he did that because he wants to show that locals and localUniverse are only used for initializing emptySet.

On the other hand, in Java you can do something like

public class SomeClass extend ParenClass{
    private int val;   

    {
        //initializztion block
        val = -1;
    }

    public SomeClass()
    {
        super();
    }

    public SomeClass(String iniName)
    {
        super(iniName);
    }   
}

The initialization block will get copy to the beginning of each of the constructors (after the super call) during compile time.

So maybe the author copy and pasted the block of code into wrong place; he copied it into the constructor instead of outside of the constructor.

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