java 实现栈

public class Stack {
    public int[] elem;
    public int usedSize;
    
    public Stack() {
        this.elem = new int[10];
    }

    //Check whether the Stack is full
    public boolean isFull() {
        return this.usedSize == this.elem.length;
    }

    //Check whether the Stack is empty
    public boolean empty() {
        return this.usedSize == 0;
    }

    //Push a value at the top of the Stack
    public void push(int val) {
        if (isFull()) {
            this.elem = Arrays.copyOf(this.elem, this.elem.length * 2);
        }
        this.elem[usedSize++] = val;
    }

    //Pop the top value of the Stack
    public int pop() {
        if (this.empty()) {
            System.out.println("栈为空!");
            return -1;
        } else {
            return this.elem[--this.usedSize];
        }
    }

    //Get the value at the top of the Stack
    public int peek() {
        if (this.empty()) {
            System.out.println("栈为空!");
            return -1;
        } else {
            return this.elem[usedSize - 1];
        }
    }
}