java堆栈应用之括号匹配

java堆栈应用之括号匹配(jdk1.6)：

package tf;

import java.util.ArrayDeque;
import java.util.Deque;

public class StackTest {

	public static void main(String[] args) {
		Deque<Character> stack = new ArrayDeque<Character>();
		String str = "ab12+[b2(eef)w-45tyf[lk6{zxc29hg}]]";
		boolean flag = true;
		char ch;
		for(int i = 0; i < str.length(); i++) {
			ch = str.charAt(i);
			if(ch == '(' || ch == '[' || ch == '{') {
				stack.offerFirst(ch);
			}
			
			else if(ch == ')') {
				if(stack.peekFirst() != null && stack.peekFirst() == '(') {
					stack.pollFirst();
				}
				else {
					flag = false;
					break;
				}
			}
			else if(ch == ']') {
				if(stack.peekFirst() != null && stack.peekFirst() == '[') {
					stack.pollFirst();
				}
				else {
					flag = false;
					break;
				}
			}
			else if(ch == '}') {
				if(stack.peekFirst() != null && stack.peekFirst() == '{') {
					stack.pollFirst();
				}
				else {
					flag = false;
					break;
				}
			}			
		}
		
		if(flag) {
			flag = stack.isEmpty();
		}
		System.out.println("是否匹配：" + flag);
	}
}