【数据结构】栈和队列

public class stack {
    private int size;
    private int[] data;
    public stack(){
        this(10);
    }
    public stack(int capacity){
        this.data = new int[capacity];
    }
    public void push(int val){
        this.data[size] = val;
        size++;
        if(size>data.length){
            this.data = Arrays.copyOf(data,data.length>>1);
        }
    }
    public int pop() throws NoSuchFieldException {
        if(size ==0){
            throw new NoSuchFieldException("stack is Null!");
        }
        int i = this.data[size-1];
        size--;
        return i;
    }
    public int peek() throws NoSuchFieldException {
        if(size ==0){
            throw new NoSuchFieldException("stack is Null!");
        }
        int i = this.data[size-1];
        return i;
    }
    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder("[");
        for(int i