Generic Queue Array Resize - Java Data Structure

Java examples for Data Structure:queue

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Description

Generic Queue Array Resize

Demo Code

import java.util.Arrays;

public class GenericQueueArrayResize<Item> {
    private int first;
    private int numelements;
    private Object[] data;

    public GenericQueueArrayResize() {
        data = new Object[1];
        first = 0;/*  w ww. jav  a 2  s .  c o m*/
        numelements = 0;
    }

    private void resize(int newsize) {
        System.out.println(String.format("Resizing array to %d", newsize));
        // resize the array
        Object[] newdata = new Object[newsize];
        for (int i = 0; i < numelements; i++) {
            newdata[i] = data[(first + i) % data.length];
            data[i] = null; // is this necessary?
        }
        first = 0;
        data = newdata; // or does this make all of data go out of scope?
    }

    public Item dequeue() {
        if (numelements == 0) {
            throw new java.util.NoSuchElementException();
        }
        Item firstval = (Item) data[first];
        data[first] = null;
        numelements -= 1;
        // check if this is the last item
        if (numelements == 0)
            first = 0;
        else {
            first = (first + 1) % data.length;
            if (numelements <= data.length / 4)
                resize(data.length / 2);
        }
        return firstval;
    }

    public void enqueue(Item s) {
        // check if array is full
        if (numelements >= data.length)
            resize(data.length * 2);
        data[(first + numelements) % data.length] = s;
        numelements += 1;
    }

    public static void main(String[] args) {
        GenericQueueArrayResize<Integer> queue = new GenericQueueArrayResize<Integer>();
        int N = Integer.parseInt(args[0]);
        double prob = Double.parseDouble(args[1]);
        // testing enqueue-dequeue
        System.out.println("********** Testing Enqueue-Dequeue **********");
        for (int i = 0; i < N; i++) {
            if (StdRandom.uniform() < prob) {
                try {
                    queue.enqueue(1);
                } catch (java.lang.ArrayIndexOutOfBoundsException e) {
                    System.out.println(Arrays.toString(queue.data));
                    throw new java.lang.ArrayIndexOutOfBoundsException();
                }
            } else {
                try {
                    queue.dequeue();
                } catch (java.util.NoSuchElementException e) { /* Ignore empty queue exception */
                }
            }
        }
    }
}

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