Java Generics Question

Question

Queue12 is an interface, QueueImp12 is an implementation of Queue12. So i'm trying to test my QueueImp12 but when i run it(it compiles) in eclipse my output gets terminated in console. I believe I created ringBuffer correctly. If my test looks fine, then something must be wrong with my implementation or eclipse. Thanks

import java.util.NoSuchElementException;


public class QueueImpl12<T> implements Queue12<T> 
{

private int _size, _backIdx, _frontIdx;
private static final int _defaultCapacity = 128;
private T[] _ringBuffer;



public QueueImpl12(int capacity)
{
    _ringBuffer = (T[]) new Object[capacity];
    clear();    
}


public QueueImpl12()
{
    _ringBuffer = (T[]) new Object[_defaultCapacity];
    clear();
}

private int wrapIdx(int index)
{

    return index % capacity();
}



public void clear() 
{
    _backIdx = 0;
    _frontIdx = 0;
    _size = 0;

}

@Override
public int capacity() 
{
    // TODO Auto-generated method stub
    return _ringBuffer.length;
}

@Override
public int size() 
{
    // TODO Auto-generated method stub
    return _size;
}

@Override
public boolean enqueue(T o) 
{
    //add o to back of queue


    if(_ringBuffer.length == _size)
    {
        return false;
    }


       _ringBuffer[_backIdx] = o;
        _backIdx = wrapIdx(_backIdx + 1 );
        _size++;





    return true;
}

@Override
public T dequeue()
{
    if(_size == 0)  //empty list
    {
        throw new NoSuchElementException();
    }

    T tempObj = _ringBuffer[_frontIdx];     //store frontIdx object
    _ringBuffer[_frontIdx] = null;          
    _frontIdx++;



    _size--;
    return tempObj;
}

@Override
public T peek() 
{

    return _ringBuffer[_frontIdx];
}

}




public class P3test  
{
public static<T> void main(String[] args) 
{
    final Queue12<T> ringBuffer = new QueueImpl12<T>();
    T o = (T) new String("this");
    ringBuffer.enqueue(o); //add element to the back
    ringBuffer.dequeue();  //remove/return element in the front

}
 }

Reformat your code. I is obvious that it won't compile now. Also main method is not a test, try JUint some day(TDD is so awesome). — Kiril Kirilov, Aug 26 '11 at 10:13
Why are you casting a `String` to `T`? That doesn't make any sense. And where is `T` coming from? — Oliver Charlesworth, Aug 26 '11 at 10:13
If it compiles, the generics part should be fine. What exactly is the problem you see? Is it supposed to output anything? — Thilo, Aug 26 '11 at 10:13
i have 2 other classes, public interface Queue12{..} andpublic class QueueImpl12 implements Queue12{..} I wanted to test it through main somehow and wasn't sure what i could put in enqueue() to test it(going to start learning Junit/TDD now). i don't understand what type is it just object type? since you can't put a string directly into enqueue, i thought making a string of type T would work. — earbulan, Aug 26 '11 at 10:26

score 2 · Accepted Answer · edited Nov 28 '12 at 22:28

That 'terminated' you have been seeing lately is the expected behavior when your program finishes.

Put some System.outs or asserts to verify that your code runs (here it runs, with some awful cast warnings, but runs)

final Queue12<T> ringBuffer = new QueueImpl12<T>();
T o = (T) new String("this");
ringBuffer.enqueue(o); //add element to the back
System.out.println(ringBuffer.peek());//this should print 'this' in the console\
//assertEquals('this', ringBuffer.peek());
ringBuffer.dequeue();  //remove/return element in the front

Learn how to use generics and tests. And don't put generic argument in main function, is is useless there.

Java Generics Question

1 Answers1