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
时间： 2024-10-08 18:14:21