棧是特殊的線性表宇葱，只能從表尾進行插入和刪除，稱為入棧和出棧猾封。
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package org.example.ch3;
/**
* stack
* @param <T> element type
*/
public class Stack<T> {
// capability of stack
private static int MAX_SIZE = 20;
private int size;
private T[] elements;
/**
* initiate empty stack.
*/
public Stack() {
size = 0;
elements = (T[]) new Object[MAX_SIZE];
}
/**
* push data into stack
* @param data data
* @return <code>true</code> if push success
*/
public boolean push(T data) {
//outage of stack
if (size > MAX_SIZE) {
return false;
}
elements[size++] = data;
return true;
}
/**
* pop data from stack.
* @return data from top of stack
*/
public T pop() {
if (size == 0) {
return null;
}
return elements[--size];
}
/**
* read top of stack.
* @return data of the stack
*/
public T getTop() {
if (size > 0) {
return elements[size - 1];
}
return null;
}
public boolean isEmpty() {
return size == 0;
}
public void clear() {
size = 0;
}
public int getSize() {
return size;
}
}
