Stack栈

java中的栈也是基于数组，和Queue不同的是Stack是后进先出即LIFO: last in first out。可以把栈想象成往箱子里放被子，最后放的被子最先被取出来。

Stack例子：判断表达式的括号、中括号、大括号的合法性

package com.test;
import java.util.Stack;
/**
 * 栈的学习
 */
public class StackLearn {
    public static void main(String[] args) {
        String str = "(<>()}))";
        System.out.println(balanced(str));
    }
    public static boolean balanced(String str) {
        Stack<Character> stack = new Stack<>();
        char[] array = str.toCharArray();
        try {
            for (char c : array) {
                if (isLeft(c)) {
                    stack.push(c);
                }
                if (isRight(c)) {
                    char tmp = stack.pop();
                    char left = getLeft(c);
                    if (tmp != left) {
                        return false;
                    }
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
            return false;
        }
        return true;
    }
    public static boolean isLeft(char c) {
        return c == '[' || c =='{' || c == '(' || c == '<';
    }
    public static boolean isRight(char c) {
        return c == ']' || c =='}' || c == ')' || c == '>';
    }
    public static char getLeft(char c) {
        char left;
        switch (c) {
            case ']':
                left = '[';
                break;
            case '}':
                left = '{';
                break;
            case ')':
                left = '(';
                break;
            default:
                left = '<';
                break;
        }
        return left;
    }
}