自定義棧

class MyStack{
	private int[] a;
	private int size;
	private int top;
	
	private final int ERROR = -1;//假設其他元素不會出現負數的前提下

	public MyStack(int size){
		this.size = size;
		a = new int[size];
		top = 0;//棧頂是幾，就說棧中有幾個元素
	}
	public boolean isFull(){
		return (top == size);
	}
	public boolean isEmpty(){
		return
 
 (top == 0);
	}
	public boolean push(int e){
		if(isFull()){
			return false;
		}else{
			a[top++] = e;
			return true;
		}
	}
	public boolean pop(){
		if(isEmpty()){
			return false;
		}else{
			top--;
			return true;
		}
	}
	public int peek(){
		if(!isEmpty()){
			return a[top-1];
		}else{
			return
 
 ERROR;//棧已經空，應該返回錯誤
		}
	}

	public void print(){
		for(int i = 0; i < top; i++){
			System.out.print(a[i] +" ");
		}
		System.out.println();
	}
}

public class Main{

	//測試
	public static void main(String[] args){
		MyStack stack = new MyStack(10);
		System.out.println("入棧：");
		stack.push(1);
		stack.
 
print();
		stack.push(2);
		stack.print();
		stack.push(3);
		stack.print();
		stack.push(4);
		stack.print();
		stack.push(5);
		stack.print();
		System.out.println();	

		System.out.println("棧頂元素： "+stack.peek());
		System.out.println("出棧：");
		while(!stack.isEmpty()){
			stack.print();
			stack.pop();
		}
		System.out.println("棧空嗎？"+stack.isEmpty());
	}
}

ArrayDeque類實現棧操作

import java.util.ArrayDeque;
import java.util.Iterator;

public class Main{
	
	public static void print(ArrayDeque stack){
		Iterator<ArrayDeque> it = stack.iterator();
		while(it.hasNext()){
			System.out.print(it.next()+" ");
		}
		System.out.println();
	}
	
	//測試
	public static void main(String[] args){
		ArrayDeque<Integer> stack = new ArrayDeque<>(10);
		System.out.println("入棧：");
		stack.push(1);
		print(stack);
		stack.push(2);
		print(stack);
		stack.push(3);
		print(stack);
		stack.push(4);
		print(stack);
		stack.push(5);
		print(stack);
		System.out.println();	

		System.out.println("棧頂元素： "+stack.peek());
		System.out.println("出棧：");
		while(!stack.isEmpty()){
			
			stack.pop();
			print(stack);
		}
		System.out.println("棧空嗎？"+stack.isEmpty());
	}
}

【例項】字串逆序

import java.util.ArrayDeque;
import java.util.Scanner;

public class Main{
	
	//測試
	public static void main(String[] args){
		ArrayDeque<Character> stack = new ArrayDeque<>(10);
		System.out.println("請輸入一字串： ");
		Scanner scan = new Scanner(System.in);
		String str = scan.nextLine();
		for(int i = 0; i < str.length(); i++){
			stack.push(str.charAt(i));
		}
		while(!stack.isEmpty()){
			System.out.print(stack.peek());
			stack.pop();
		}
	}
}

另外，字串逆序可以直接呼叫StringBuffer的reverse方法即可：

import java.util.Scanner;

public class Main{
	
	//測試
	public static void main(String[] args){
		System.out.println("請輸入一字串： ");
		Scanner scan = new Scanner(System.in);
		StringBuffer str = new StringBuffer(scan.next());
		System.out.println(str.reverse());
	}
}

【例項】括號匹配問題

/*
	用棧來解決括號匹配問題：
	
	針對字串中的每個字元，
	（1）如果是(,[,{入棧；
	（2）如果是非括號，不入棧；
	（3）如果是),],}，取出棧頂元素，比較棧頂元素和當前字元是否匹配，如果不匹配，可得出結論：不匹配；
	（4）如果所有字元已經完成棧操作，棧中仍然有剩餘的元素，可得出結論：不匹配；
	（5）除了以上不匹配情況外，得出結論：匹配。

*/

import java.util.Scanner;
import java.util.ArrayDeque;

public class Main{
	
	//測試
	public static void main(String[] args){
		Scanner scan = new Scanner(System.in);
		
		ArrayDeque<Character> stack = new ArrayDeque<>();
		
		String str = null;
		System.out.println("請輸入一字串： ");
		while(scan.hasNextLine()){
			stack.clear();
			str = scan.nextLine();
			boolean flag = true;
			for(int i = 0; i < str.length(); i++){
				Character c = str.charAt(i);
				Character top = stack.peek();
				
				switch(c){
					case '[': 
					case '(':
					case '{': 
						stack.push(c);
						break;
					case ')': 
						if(top != null && top == '('){
							stack.pop();
						}else{
							flag = false;
						}
						break;
					case ']': 
						if(top != null && top == '['){
							stack.pop();
						}else{
							flag = false;
						}
						break;
					case '}': 
						if(top != null && top == '{'){
							stack.pop();
						}else{
							flag = false;
						}
						break;
					default:	break;
				}
				if(!flag){
					break;
				}
			}
			if(!stack.isEmpty() || !flag){
				System.out.println("not correct");
			}else{
				System.out.println("correct");
			}
			System.out.println("請輸入一字串： ");
		}
	}
}