Java实现中缀表达式转换为后缀表达式

实现中缀表达式转换为后缀表达式主要包含三个类，一个主函数，一个自定义栈的类，还有一个就是核心类，实现其转换。
一、自定义栈的类

package date0617;

/**
 *@author TonyJ
 *@time 2011-6-17 下午02:24:47
 */
public class MyStack {
	private int maxSize;//栈的最大容量
	private char[] ch;	//栈的数据
	private int top;	//栈头标记

	public MyStack(int s) {
		maxSize = s;
		ch = new char[s];
		top = -1;
	}

	public void push(char c) {//入栈
		ch[++top] = c;
	}

	public char pop() {//出栈
		return ch[top--];
	}

	public char peek() {
		return ch[top];
	}

	public boolean isEmpty() {
		return top == -1;
	}

	public boolean isFull() {
		return top == (maxSize - 1);
	}

	public int size() {
		return top + 1;
	}

	public char get(int index) {
		return ch[index];
	}

	public void display(String str) {
		System.out.print(str);
		System.out.print(" Stack (bottom-->top): ");
		for (int i = 0; i < size(); i++) {
			System.out.print(get(i)+" ");
		}
		System.out.println();
	}
}

二、核心实现类

package date0617;

/**
 *@author TonyJ
 *@time 2011-6-17 下午02:43:48
 */
public class InToPost {
	private MyStack ms;//自定义栈
	private String input;//输入中缀表达式
	private String output="";//输出的后缀表达式

	public InToPost(String input) {
		this.input = input;
		int size = input.length();
		ms = new MyStack(size);
	}

	public String doTrans() {//转换为后缀表达式方法
		for (int i = 0; i < input.length(); i++) {
			char ch = input.charAt(i);
			ms.display("for " + ch + " ");
			switch (ch) {
			case '+':
			case '-':
				getOper(ch, 1);
				break;
			case '*':
			case '/':
				getOper(ch, 2);
				break;
			case '(':
				ms.push(ch);
				break;
			case ')':
				getParent(ch);
				break;
			default:
				output = output + ch;
				break;
			}//end switch 
		}//end for
		while(!ms.isEmpty()){
			ms.display("While ");
			output=output+ms.pop();
		}
		ms.display("end while!!");
		return output;
	}
	
	/**
	 * @param ch
	 * 获得上一级字符串
	 */
	public void getParent(char ch) {
		while(!ms.isEmpty()){
			char chx=ms.pop();
			if(chx=='('){
				break;
			}else{
				output=output+chx;
			}
		}
	}

	/**
	 * @param ch 操作符
	 * @param prec1 操作符的优先级
	 * 根据操作符的优先级判断是否入栈，及入栈的顺序
	 */
	public void getOper(char ch, int prec1) {
		while (!ms.isEmpty()) {//判断栈是否为空
			char operTop = ms.pop();
			if (operTop == '(') {
				ms.push(operTop);
				break;
			} else {
				int prec2;
				if (operTop == '+' || operTop == '-') {
					prec2 = 1;
				} else {
					prec2 = 2;
				}
				if (prec2 <prec1) {
					ms.push(operTop);
					break;
				} else {
					output = output + operTop;
				}
			}
		}// end while
		ms.push(ch);
	}
}

三、主类代码

package date0617;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

/**
 *@author TonyJ
 *@time 2011-6-17 下午03:44:49
 */
public class InfixMain {
	public static void main(String[] args) {
		String input, output;
		while (true) {
			input = getString();
			if ("".equals(input) || input == null) {
				break;
			}
			InToPost itp = new InToPost(input);
			output = itp.doTrans();
			System.out.println("Profix is " + output + "\n");
		}
	}

	public static String getString() {
		String output = "";
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		try {
			System.out.println("请输入算术表达式：");
			output = br.readLine();
		} catch (IOException e) {
			e.printStackTrace();
		}
		return output;
	}
}

输入的表达式为：A*(B+C)-D/(E+F)
执行的结果如下：
请输入算术表达式：
A*(B+C)-D/(E+F)
for A  Stack (bottom-->top):
for *  Stack (bottom-->top):
for (  Stack (bottom-->top): *
for B  Stack (bottom-->top): * (
for +  Stack (bottom-->top): * (
for C  Stack (bottom-->top): * ( +
for )  Stack (bottom-->top): * ( +
for -  Stack (bottom-->top): *
for D  Stack (bottom-->top): -
for /  Stack (bottom-->top): -
for (  Stack (bottom-->top): - /
for E  Stack (bottom-->top): - / (
for +  Stack (bottom-->top): - / (
for F  Stack (bottom-->top): - / ( +
for )  Stack (bottom-->top): - / ( +
While  Stack (bottom-->top): - /
While  Stack (bottom-->top): -
end while!! Stack (bottom-->top):
Profix is ABC+*DEF+/-