经典例题：模仿栈

测试类：

class Test {
    public static void main(String[] args) throws StackOperationException{
        Stack st = new Stack();
        try {
            st.push(new User("hl",1));
            st.push(new User("hf",2));
            st.push(new User("yx",3));
            st.push(new User("hx",4));
            st.push(new User("ll",5));
        }catch(Exception e) {
            e.printStackTrace();
        }
        try {
            System.out.println(st.pop());
            System.out.println(st.pop());
            System.out.println(st.pop());
            System.out.println(st.pop());
            System.out.println(st.pop());
        }catch(Exception e) {
            e.printStackTrace();
        }
    }
}

栈类：

class Stack{
    Object[] elements;
    int index;
    Stack(){
        this(5);
    }
    Stack(int max){
        elements = new Object[max];
    }
    public void push(Object element) throws StackOperationException {
        if(index == elements.length) {
            throw new StackOperationException("越栈");
        }
        else {
            elements[index++] = element;
        }
        
    }
    public Object pop() throws StackOperationException {
        if(index == 0) {
            throw new StackOperationException("栈空");
        }
        else {
            Object element = elements[--index];
            return element;
        }
    }
}

自定义异常：

class StackOperationException extends Exception{
    
    public StackOperationException() {}
    
    public StackOperationException(String msg) {
        
        super (msg);
    }
}

添加用户类：

class User{
    String name;
    int age;
    User(String name,int age){
        this.name = name;
        this.age = age;
    }
    public String toString() {
        return name + " " + age;
    }
}