栈是存放对象的一种特殊容器，在插入与删除对象时，这种结构遵循后进先出（ Last-in-first-out，LIFO）的原则。java本身是有自带Stack类包，为了达到学习目的已经更好深入了解stack栈，自己动手自建java stack类是个很好的学习开始：
自建Java Stack 类
Stack 类：
1 package com.stack; 2 3 import java.util.ArrayList; 4 import java.util.Arrays; 5 6 /** 7 * Stack Class 8 * @author ganyee 9 * 10 */ 11 public class Stack { 12 //Define capacity constant:CAPACITY 13 private static final int CAPACITY = 1024; 14 //Define capacity 15 private static int capacity; 16 //Define the top position of stack 17 //top = -1 meaning that the stack empty 18 private static int top = -1; 19 //Basic Object class array 20 Object[] array; 21 //Initialize the capacity of stack 22 public Stack() { 23 this.capacity = CAPACITY; 24 array = new Object[capacity]; 25 } 26 27 //Get the size of stack 28 public int getSize(){ 29 if(isEmpty()){ 30 return 0; 31 }else{ 32 return top + 1; 33 } 34 } 35 36 //Get whether stack is empty 37 public boolean isEmpty(){ 38 return (top < 0); 39 } 40 41 //Get the top element of stack 42 public Object top() throws ExceptionStackEmpty{ 43 44 if(isEmpty()){ 45 throw new ExceptionStackEmpty("Stack is empty"); 46 } 47 return array[top]; 48 49 } 50 51 //Push element to stack 52 public void push(Object element) throws ExceptionStackFull{ 53 if(getSize()== CAPACITY){ 54 throw new ExceptionStackFull("Stack is full"); 55 } 56 array[++ top] = element; 57 } 58 59 //Pop element from stack 60 public Object pop() throws ExceptionStackEmpty{ 61 if(isEmpty()){ 62 throw new ExceptionStackEmpty("Stack is empty"); 63 } 64 return array[top --]; 65 } 66 67 //Get the all elements of stack 68 public String getAllElements() throws ExceptionStackEmpty{ 69 String[] arr = new String[top + 1]; 70 if(!isEmpty()){ 71 for(int i = 0;i < getSize();i ++){ 72 arr[i] = (String)array[i]; 73 } 74 } 75 return Arrays.toString(arr); 76 } 77 }
自定义ExceptionStackEmpty异常类
1 package com.stack; 2 3 public class ExceptionStackEmpty extends Exception { 4 5 //Constructor 6 public ExceptionStackEmpty(){ 7 8 } 9 10 //Define myself exception construct with parameters 11 public ExceptionStackEmpty(String string){ 12 super(string); 13 } 14 }
自定义ExceptionStackFull异常类
1 package com.stack; 2 3 public class ExceptionStackFull extends Exception { 4 5 //Constructor 6 public ExceptionStackFull(){ 7 8 } 9 10 //Define myself exception construct with parameters 11 public ExceptionStackFull(String string){ 12 super(string); 13 } 14 }
测试类:
1 package com.stack; 2 3 public class StackTest { 4 5 public static void main(String[] args) { 6 // TODO Auto-generated method stub 7 Stack stack= new Stack(); 8 System.out.println(stack.getSize()); 9 System.out.println(stack.isEmpty()); 10 try { 11 stack.push(8); 12 stack.push(3); 13 stack.push(4); 14 stack.push(7); 15 stack.push(1); 16 stack.push(8); 17 stack.push(3); 18 stack.push(4); 19 stack.push(7); 20 stack.push(1); 21 System.out.println(stack.getSize()); 22 System.out.println(stack.top()); 23 System.out.println(stack.getAllElements()); 24 25 System.out.println(stack.pop()); 26 System.out.println(stack.pop()); 27 System.out.println(stack.pop()); 28 System.out.println(stack.pop()); 29 System.out.println(stack.pop()); 30 System.out.println(stack.pop()); 31 System.out.println(stack.pop()); 32 System.out.println(stack.pop()); 33 System.out.println(stack.pop()); 34 System.out.println(stack.pop()); 35 36 } catch (ExceptionStackFull e) { 37 // TODO Auto-generated catch block 38 e.printStackTrace(); 39 }catch (ExceptionStackEmpty e) { 40 // TODO Auto-generated catch block 41 e.printStackTrace(); 42 } 43 } 44 45 }
测试结果：
0 true 10 1 [8, 3, 4, 7, 1, 8, 3, 4, 7, 1] 1 7 4 3 8 1 7 4 3 8
栈的应用：符号匹配
下面，我们将借助一个栈结构 S，通过对算术表达式自左向右的一遍扫描，检查其中的括号是否匹配。
假设算术表达式为 X = “x0x1x2…xn-1”，其中 xi 可以是括号、常数、变量名或者算术运算符。我们依次检查 X 中的各个符号，非括号的符号都可以忽略。若遇到左括号，则将其压入栈 S 中；若遇到右括号，则将栈顶符号弹出并与该右括号对比。如果发现某对括号不匹配，或者遇到右括号时栈为空，或者整个表达式扫描过后栈非空，都可以断定括号不匹配。
在按照以上规则扫描完所有字符后，若栈为空，则说明括号是匹配的。如果按照前面对栈的实现，每一 push()和 pop()操作都只需常数时间，因此对于长度为 n 的算术表达式，上述算法需要运行 O(n)的时间。
该算法的伪代码描述如 算法二.1 所示：
1 package com.stack; 2 3 public class MatchClass { 4 5 public static boolean Match(String str) throws ExceptionStackFull, ExceptionStackEmpty{ 6 Stack stack = new Stack(); 7 str = str.replaceAll(" ",""); 8 char s; 9 for(int i = 0;i < str.length();i ++){ 10 if(str.charAt(i) == '(' || str.charAt(i) == '{' || str.charAt(i) == '[') 11 stack.push(str.charAt(i)); 12 else{ 13 if(stack.isEmpty()) 14 return false; 15 else{ 16 s = str.charAt(i); 17 switch(s){ 18 case ')': 19 if((Character)stack.pop() != '(') 20 return false; 21 break; 22 case '}': 23 if((Character)stack.pop() != '{') 24 return false; 25 break; 26 case ']': 27 if((Character)stack.pop() != '[') 28 return false; 29 break; 30 } 31 } 32 33 } 34 } 35 if(stack.isEmpty()){ 36 return true; 37 }else{ 38 return false; 39 } 40 } 41 }
1 package com.stack; 2 3 public class ParentMatch { 4 5 public static void main(String[] args) { 6 7 MatchClass match = new MatchClass(); 8 //String str = "()({})"; //Match 9 //String str = "()({}) {([()[]])}";//Match 10 //String str = "([]{)";//Not match 11 //String str = ")([()] {}";//Not match 12 String str = "([())]{}";//Not match 13 try { 14 if(!match.Match(str)){ 15 System.out.println(str + ": Not Macth"); 16 }else{ 17 System.out.println(str + ": Macth"); 18 } 19 } catch (ExceptionStackFull e) { 20 // TODO Auto-generated catch block 21 e.printStackTrace(); 22 } catch (ExceptionStackEmpty e) { 23 // TODO Auto-generated catch block 24 e.printStackTrace(); 25 } 26 } 27 28 }
测试结果：
()({}): Macth
()({}) {([()[]])}: Macth
([]{): Not Macth
)([()] {}: Not Macth
([())]{}: Not Macth