Java – queue implementation using circular arrays: which method can you adjust the size of circular arrays?

I'm using a circular array to implement a queue, and I'm a little stuck in the resize () method implementation (when the array is full)

In the enqueue () method, I check whether the size of the array is equal to its length, and if it is full, I check it Now, instead of throwing an exception, I try to resize the array

The problem is, I have two cases to consider

>What is the best way to copy the elements of the old array to the new larger array?

I think it uses a for loop, such as:

newArray = new Array[oldArray.length*2];

if (front <= rear) {
    for (int i = front; i < rear; i++) {
        newArray[i] = oldArray[i];
    } 
} else {
    for (int i = front; i < newArray.length; i++) {
        newArray[i] = oldArray[i];
    }

    for (int j = rear; j < front; j++) {
        // i'm using the variable i,the order is maintained
        newArray[i] = oldArray[j];
        i++;
    }
}

Then oldarray = newarray, return newarray and resize

I'm not sure how much to do it. I'm afraid I'll lose my values

Can someone tell me if there is a better way?

Solution

To copy an array with multiple elements, use system Arraycopy (), because it is usually implemented as native code, for example, sun's VM uses a manually encoded assembler

Front > rear

Because the data is continuous, it can remain in the same position in the new array

System.arraycopy(oldArray,front,newArray,front-rear);

The preceding < = the following data is discontinuous, so copy the two blocks to the beginning of the new array

// copy [rear to end]
System.arraycopy(oldArray,rear,oldArray.length-rear);
// copy [0 to front]
System.arraycopy(oldArray,oldArray.length-rear,front);
front = oldArray.length-(rear-front);
rear = 0;