Java棧實現__Java

棧數組實現一：優點：入棧和出棧速度快，缺點：長度有限(有時候這也不能算是個缺點)

public class Stack {private int top = -1;private Object[] objs;public Stack(int capacity) throws Exception{if(capacity < 0)throw new Exception("Illegal capacity:"+capacity);objs = new Object[capacity];}public void push(Object obj) throws Exception{if(top == objs.length - 1)throw new Exception("Stack is full!");objs[++top] = obj;}public Object pop() throws Exception{if(top == -1)throw new Exception("Stack is empty!");return objs[top--];}public void dispaly(){System.out.print("bottom -> top: | ");for(int i = 0 ; i <= top ; i++){System.out.print(objs[i]+" | ");}System.out.print("\n");}public static void main(String[] args) throws Exception{Stack s = new Stack(2);s.push(1);s.push(2);s.dispaly();System.out.println(s.pop());s.dispaly();s.push(99);s.dispaly();s.push(99);}}

bottom -> top: | 1 | 2 | 2bottom -> top: | 1 | bottom -> top: | 1 | 99 | Exception in thread "main" java.lang.Exception: Stack is full!at Stack.push(Stack.java:17)at Stack.main(Stack.java:44)

資料項目入棧和出棧的時間複雜度都為常數O(1)

棧數組實現二：優點：無長度限制，缺點：入棧慢

import java.util.Arrays;public class UnboundedStack {private int top = -1;private Object[] objs;public UnboundedStack() throws Exception{this(10);}public UnboundedStack(int capacity) throws Exception{if(capacity < 0)throw new Exception("Illegal capacity:"+capacity);objs = new Object[capacity];}public void push(Object obj){if(top == objs.length - 1){this.enlarge();}objs[++top] = obj;}public Object pop() throws Exception{if(top == -1)throw new Exception("Stack is empty!");return objs[top--];}private void enlarge(){int num = objs.length/3;if(num == 0)num = 1;objs = Arrays.copyOf(objs, objs.length + num);}public void dispaly(){System.out.print("bottom -> top: | ");for(int i = 0 ; i <= top ; i++){System.out.print(objs[i]+" | ");}System.out.print("\n");}public static void main(String[] args) throws Exception{UnboundedStack us = new UnboundedStack(2);us.push(1);us.push(2);us.dispaly();System.out.println(us.pop());us.dispaly();us.push(99);us.dispaly();us.push(99);us.dispaly();}}

bottom -> top: | 1 | 2 | 2bottom -> top: | 1 | bottom -> top: | 1 | 99 | bottom -> top: | 1 | 99 | 99 | 

由於該棧是由數組實現的，數組的長度是固定的，當棧空間不足時，必須將原數組資料複製到一個更長的數組中，考慮到入棧時或許需要進行數組複製，平均需要複製N/2個資料項目，故入棧的時間複雜度為O(N)，出棧的時間複雜度依然為O(1)

棧單鏈表實現：沒有長度限制，並且出棧和入棧速度都很快

public class LinkedList {private class Data{private Object obj;private Data next = null;Data(Object obj){this.obj = obj;}}private Data first = null;public void insertFirst(Object obj){Data data = new Data(obj);data.next = first;first = data;}public Object deleteFirst() throws Exception{if(first == null)throw new Exception("empty!");Data temp = first;first = first.next;return temp.obj;}public void display(){if(first == null)System.out.println("empty");System.out.print("top -> bottom : | ");Data cur = first;while(cur != null){System.out.print(cur.obj.toString() + " | ");cur = cur.next;}System.out.print("\n");}}

public class LinkedListStack {private LinkedList ll = new LinkedList();public void push(Object obj){ll.insertFirst(obj);}public Object pop() throws Exception{return ll.deleteFirst();}public void display(){ll.display();}public static void main(String[] args) throws Exception{LinkedListStack lls = new LinkedListStack();lls.push(1);lls.push(2);lls.push(3);lls.display();System.out.println(lls.pop());lls.display();}}

top -> bottom : | 3 | 2 | 1 | 3top -> bottom : | 2 | 1 | 

資料項目入棧和出棧的時間複雜度都為常數O(1)