java achieve the realization of the stack

Reprinted Original: https://blog.csdn.net/weixin_43533825/article/details/96708590

 

Stack: LIFO (Last In First Out), own realization of a stack, the stack has the required push (), pop () (returns the top element and the stack), peek () (returns the top element not stack), isEmpty ( ) these basic methods.

 

The third recommended

 

First, using the array to achieve stack

Tip: first determine the stack before each stack capacity is enough, if not enough to use Arrays.copyOf () for expansion

java.util.Arrays Import;
 / * * 
 * achieve stack array 
 * @param <T> 
 * / 
class Mystack1 <T> {
     // Array stack implemented 
    private Object [] Stack;
     // array size -> stack 
    private  int size; 
 
    Mystack1 () { 
        Stack = new new Object [ 10 ]; // initial capacity 10 
    } 
 
    // determines whether an empty 
    public Boolean isEmpty () 
    { 
        return size == 0 ; 
    } 
 
    // returns the top element 
    public T PEEK () 
    {
        T t = null;
        if (size > 0)
            t = (T) stack[size - 1];
        return t;
    }
    
    //压栈
    public void push(T t) 
    {
        expandCapacity(size + 1);
        stack[size] = t;
        size++;
    }
 
    //出栈
    public T pop() {
        T t = peek();
        if (size > 0) {
            stack[size - 1] = null;
            size--;
        }
        return t;
    }
 
    //扩大容量
    public void expandCapacity(int size) {
        int len = stack.length;
        if (size > len) {
            size = size * 3 / 2 + 1;//每次扩大50%
            stack = Arrays.copyOf(stack, size);
        }
    }
}
 
public class ArrayStack {
    public static void main(String[] args) {
        Mystack1<String> stack = new Mystack1<>();
        System.out.println(stack.peek());
        System.out.println(stack.isEmpty());
        stack.push("java");
        stack.push("is");
        stack.push("beautiful");
        stack.push("language");
        System.out.println("pop-->"+stack.pop());
        System.out.println("pop-->"+stack.pop());
        System.out.println("pop-->"+stack.pop());
        System.out.println("stack.isEmpty-->"+stack.isEmpty());
        System.out.println("pop-->"+stack.pop());
        System.out.println("stack.isEmpty-->"+stack.isEmpty());
        System.out.println("peek-->"+stack.peek());
    }
}

 

 

Second, the realization of the stack using a linked list

com.icil.elsa.test Package;
 / * * 
 *-way linked list implementation stack 
 * @param <T> 
 * / 
class Mystack2 <T> {
     // definition of the linked list 
    class the Node <T>  
    { 
        Private T T;
         Private the Node Next; 
    } 
 
    Private the Node <T> head = null ; 
 
    // constructor initializes head pointer
 //     Mystack2 () {
 //         head = null;
 //     } 
 
    // stack 
    public  void Push (T T) {
         IF (T == null ) 
        { 
            the throw new NullPointerException("参数不能为空");
        }
        if (head == null) 
        {
            head = new Node<T>();
            head.t = t;
            head.next = null;
        } else 
        {
            Node<T> temp = head;
            head = new Node<>();
            head.t = t;
            head.next = temp;
        }
    }
 
    //出栈
    public T pop() 
    {
        if(head==null)
        {
          return null;
        }
        T t = head.t;
        head = head.next;
        return t;
    }
 
    //栈顶元素
    public T peek() {
        T t = head.t;
        return t;
    }
 
    //栈空
    public boolean isEmpty() {
        if (head == null)
            return true;
        else
            return false;
    }
}
 
public class LinkStack {
    public static void main(String[] args) {
        Mystack2 stack = new Mystack2();
        System.out.println(stack.isEmpty());
        stack.push("java");
        stack.push("is");
        stack.push("beautiful");
        stack.push("language");
        System.out.println("pop-->"+stack.pop());
        System.out.println("pop-->"+stack.pop());
        System.out.println("pop-->"+stack.pop());
        System.out.println("stack.isEmpty-->"+stack.isEmpty());
        System.out.println("pop-->"+stack.pop());
        System.out.println("stack.isEmpty-->"+stack.isEmpty());
    }
}

 

 

Third, the use LinkedList achieve stack

• push-----addFirst()
• pop-------removeFirst()
• peek-----getFirst()
• isEmpty-isEmpty()

package com.icil.elsa.test;

import java.util.LinkedList;

/**
 * LinkedList实现栈
 *
 * @param <T>
 */
class ListStack<T> {
    private LinkedList<T> ll = new LinkedList<>();
 
    //入栈
    public void push(T t) {
        ll.addFirst(t);
    }
 
    //出栈
    public T pop() {
        return ll.removeFirst();
    }
 
    //栈顶元素
    public T peek() {
        T t = null;
        //Direct access to the elements will be reported anomaly, it is necessary to determined whether the air 
        IF (! Ll.isEmpty ()) 
            T = ll.getFirst ();
         return T; 
    } 
 
    // stack empty 
    public Boolean isEmpty () {
         return ll.isEmpty () ; 
    } 
} 
 
public  class LinkedListStack {
     public  static  void main (String [] args) { 
        ListStack <String> Stack = new new ListStack (); 
        the System. OUT .println (stack.isEmpty ()); 
        . the System OUT .println (Stack. PEEK ()); 
        stack.push ("java");
        stack.push("is");
        stack.push("beautiful");
        stack.push("language");
        System.out.println("pop-->"+stack.pop());
        System.out.println("pop-->"+stack.pop());
        System.out.println("pop-->"+stack.pop());
        System.out.println("stack.isEmpty-->"+stack.isEmpty());
        System.out.println("pop-->"+stack.pop());
        System.out.println("stack.isEmpty-->"+stack.isEmpty());
    }

}