Java数据结构--基于数组的队列

public class Queue {

    private int[] data;

    private int head;
    private int back;
    private int size;
 
    public Queue(){
        data = new int[20];

    }
    public void append(int x){
        if(this.size == data.length -1){
            copy();
        }
        data[back] = x;
        back = (back+1)%data.length;
        size += 1;
    }
    public int peek(){
        size -= 1;
        int y = data[head];
        head = (head+1)%data.length;
        return y;
    }
    private void copy(){
        int[] data_new = new int[size*2];
        for(int i=0;i<data.length;i++){
            data_new[i] = data[i];
        }
        this.data = data_new;
    }
}