Java CircularArrayQueue isEmpty method

Question

I am trying to implement a CircularArrayQueue and my method isEmpty() is returning false when the queue isn't populated. Can you point out my error?

public CircularArrayQueue(int size)
{
    array = new Integer[size];
    front = rear = 0;
}

... code omitted 

// returns the number of elements in the queue
@Override
public int noItems() 
{   
    return array.length - getCapacityLeft();
}

// returns true if the queue is empty
@Override
public boolean isEmpty()
{
    return noItems() == 0;
}

//returns the number of available spots in the queue before a resize needs to be done
public int getCapacityLeft()
{
    return (array.length - rear + front)%array.length;
}

you posted the same question yesterday?

Vijayan Kani
– Vijayan Kani

2017-03-07 09:03:51 +00:00
Commented Mar 7, 2017 at 9:03 — Vijayan Kani
– Vijayan Kani, Commented Mar 7, 2017 at 9:03

Pete Kirkham · Accepted Answer · 2017-03-07 09:05:15Z

1

When the queue is initialised, front and rear are both zero.

public int getCapacityLeft()
{
    return (array.length - rear + front)%array.length;
}

So getCapacityLeft returns (array.length + 0)%array.length which is zero.

You need to calculate the number of items correctly, taking into account how you manage the difference between a full buffer and an empty buffer - it seems that in both cases you are using rear == front. Decide how you will tell the difference and then you can write a getCapacityLeft which returns array.length if the buffer is empty and zero if it is full.

answered Mar 7, 2017 at 9:05

Pete Kirkham

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Comments

chengpohi · Accepted Answer · 2017-03-07 08:59:36Z

0

return (array.length - rear + front)%array.length;

The above code, when array size is 0, getCapacityLeft will throw ArithmeticException. for not enable divide by zero.

answered Mar 7, 2017 at 8:59

chengpohi

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Comments

Majeed Khan · Accepted Answer · 2017-03-07 08:56:40Z

0

try

public int getCapacityLeft(){

return array.length - Math.abs(front - rear) + 1;

}

answered Mar 7, 2017 at 8:56

Majeed Khan

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Comments

Dhiral Kaniya · Accepted Answer · 2017-03-07 09:04:04Z

0

try this

    if(front == -1 && rear == -1)
         return ture;
    else
         return false;

answered Mar 7, 2017 at 9:04

Dhiral Kaniya

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1 Comment

Unamata Sanatarai Over a year ago

so... return (front == -1 && rear == -1)

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