ex2.java

该程序可将一个四则混合运算分解成一组四元式指令。

/**
 * 该类的主要任务是生成四元式
 * 设置操作符的优先级
 * 将操作符从表达式中提取出来，将操作符及其相关信息挂到列表中，并进行去括号处理
 * 
 */
package ex2;

import java.util.LinkedList;

/**
 * @author 阿赞
 *
 */
public class EX2 {
	private int length;//表达式的长度
	private int[] suffix;//四元式的结果表示符号的下标数组
	private String expression;//表达式
	Operator operator;//创建Operator类对象
	LinkedList list = new LinkedList();//用来储存操作符及其相关信息
	LinkedList list1 = new LinkedList();//用来储存四元式
	public EX2(String expression) {//构造方法
		this.expression = expression;
		length = this.expression.length();
		suffix = new int[length];
		Operator();
		Create();
	}
	public int PRI(char c) {//设置操作符的优先级
		if(c == '=') {// = 的优先级为 1
				return 1;
		}
		else if(c == '+'||c == '-') {// + 和 - 的优先级为 2
			return 2;
		}
		else if(c == '*'||c == '/') {// * 和 / 的优先级为 3
			return 3;
		}
		else if(c == '('||c == ')') {// ( 和 ) 的优先级为 4
			return 4;
		}
		else {
			return 0;
		}
	}
	public int Operator() {//将操作符从表达式中提取出来，将操作符及其相关信息挂到列表中，并进行去括号处理
		for(int i =0;i < length;i++) {
			char op = expression.charAt(i);//获取表达式的第i个字符
			if(op == '='||op == '+'||op == '-'||op == '*'||op == '/'||op == '('||op == ')') {
				operator = new Operator(""+op,i,PRI(op));//创建Operator类对象，以操作符、操作符在表达式中的下标、操作符的优先级为实参
				list.add(operator);//将Operator类的对象加到列表list尾部
			}
		}
		
		int term = 0;//权值
		for(int i = 0;i < list.size();i++) {//进行去括号处理，将括号操作符及其相关信息从列表中移除，对括号内的非括号操作符进行加权
			Operator op =(Operator)list.get(i);//获取list中第i个元素
			if(op.Get_op().equals("(")) {//遇到一个"("，权值加4
				term = term + 4;
				list.remove(i);//从列表list中移除第i个元素
				i--;//循环变量减1
			}
			else if(op.Get_op().equals(")")) {//遇到一个")"，权值减4
				term = term - 4;
				list.remove(i);
				i--;
			}
			else if(term != 0) {
				int pri = op.Get_pri() + term;
				op.Set_pri(pri);
				list.remove(i);
				list.add(i,op);
			}
		}
		System.out.println(list.size());
		/*for(int i = 0;i < list.size();i++) {
			operator = (Operator)list.get(i);
			System.out.println(operator.Get_op());
			System.out.println(operator.Get_suffix());
			System.out.println(operator.Get_pri());
		}*/
		return list.size();
	}
	public void Create() {//生成四元式
		int size = list.size();//获取表达式列表的长度
		int i = 0;//控制while循环的循环变量
		int NO = 1;//四元式的结果表示符号的下标
		while(true) {//当i=size时，结束循环
			if(list.size() == 1) {
				Operator operator1 = (Operator)list.get(0);//获取第1个操作符，也是最后一个需要处理的操作符，即"="
				
				if(expression.charAt(operator1.Get_suffix() + 1) == 'T') {
					//生成四元式
					String string = "("+operator1.Get_op()+","+"T"+(--NO)+","+0+","+expression.charAt(0)+")";
					
					list1.add(string);//将四元式挂到列表list1的尾部
					System.out.println(string);
					list.remove(0);//将操作符从列表list中移除
					//System.out.println(operator1.Get_op());
					//break;
				}
				else {
					String str = expression.substring(operator1.Get_suffix() + 1);
					String string = "("+operator1.Get_op()+","+str+","+0+","+expression.charAt(0)+")";
					list1.add(string);//将四元式挂到列表list1的尾部
					System.out.println(string);
					list.remove(0);//将操作符从列表list中移除
					//System.out.println(operator1.Get_op());
					//break;
				}
				
			}
			else if(list.size() == 2) {
				Operator operator1 = (Operator)list.get(0);//获取操作符
				Operator operator2 = (Operator)list.get(1);
				int pri1 = operator1.Get_pri();//获取操作符的优先级
				int pri2 = operator2.Get_pri();
				if(pri1 < pri2) {//处理优先级高的操作符
					
					//将表达式拆分成几个子串
					String str1 = expression.substring(operator1.Get_suffix()+1,
							operator2.Get_suffix());
					String str2 = expression.substring(operator2.Get_suffix()+1);
					String str3 = expression.substring(0,operator1.Get_suffix()+1);
					
					String str = new String();
					
					for(int k = 0;k < str1.length();k++) {
						if(str1.charAt(k) == '(') {
							str1 = str1.substring(k + 1);//消除括号
							k--;
						}
					}
					for(int k = 0;k < str2.length();k++) {
						if(str2.charAt(k) == ')') {
							str2 = str2.substring(0,k);//消除括号
						}
					}
					
					/*
					System.out.println(expression);
					for(int k = 0;k < suffix.length;k++) {
						System.out.print(suffix[k]);
					}
					System.out.println();
					*/
					
					for(int k = 1;k < str2.length() + operator2.Get_suffix() - operator1.Get_suffix();k++) {
						if(expression.charAt(k + operator1.Get_suffix()) != 'T') {
							suffix[k + operator1.Get_suffix()] = NO;//修改四元式的结果表示符号的下标数组中的相应元素
						}
					}
					
					//当前要处理的操作符左右两边的数据都为已经处理过的结果
					if(expression.charAt(operator2.Get_suffix() - 1) == 'T' && expression.charAt(operator2.Get_suffix() + 1) == 'T') {
						String string = "("+operator2.Get_op()+","+"T"+suffix[operator2.Get_suffix() - 1]+","+"T"+suffix[operator2.Get_suffix() + 1]+","+"T"+suffix[operator2.Get_suffix()]+")";
						list1.add(string);
						System.out.println(string);
					}
					
					//当前要处理的操作符左边的数据都为已经处理过的结果
					else if(expression.charAt(operator2.Get_suffix() - 1) == 'T') {
						String string = "("+operator2.Get_op()+","+"T"+suffix[operator2.Get_suffix() - 1]+","+str2+","+"T"+suffix[operator2.Get_suffix()]+")";
						list1.add(string);
						System.out.println(string);
					}
					
					//当前要处理的操作符右边的数据都为已经处理过的结果
					else if(expression.charAt(operator2.Get_suffix() + 1) == 'T') {
						String string = "("+operator2.Get_op()+","+str1+","+"T"+suffix[operator2.Get_suffix() + 1]+","+"T"+suffix[operator2.Get_suffix()]+")";
						list1.add(string);
						System.out.println(string);
					}
					
					//当前要处理的操作符左右两边的数据都未被处理过
					else {
						String string = "("+operator2.Get_op()+","+str1+","+str2+","+"T"+NO+")";
						list1.add(string);
						System.out.println(string);
					}
					
					for(int k = 1;k < str2.length() + operator2.Get_suffix() - operator1.Get_suffix();k++) {
						str = str.concat("T");//将处理过的数据和操作符置换成字符T
						suffix[k + operator1.Get_suffix()] = NO;
					}
					NO++;//四元式的结果表示符号的下标加1
					expression = str3.concat(str);//合并成新的表达式，未处理部分保持不变
					//System.out.println(expression);
					list.remove(1);//将已处理的操作符移除操作符列表
					//System.out.println(operator2.Get_op());
				}
				else {
					list.remove(0);
					//System.out.println(operator1.Get_op());
				}
			}
			else if(list.size() == 3) {
				Operator operator1 = (Operator)list.get(0);//获取操作符
				Operator operator2 = (Operator)list.get(1);
				Operator operator3 = (Operator)list.get(2);
				int pri1 = operator1.Get_pri();//获取操作符的优先级
				int pri2 = operator2.Get_pri();
				int pri3 = operator3.Get_pri();
				if(pri1 < pri2 && pri2 >= pri3) {//处理优先级高的操作符
					
					//将表达式拆分成几个子串
					String str1 = expression.substring(operator1.Get_suffix()+1,
							operator2.Get_suffix());
					String str2 = expression.substring(operator2.Get_suffix()+1,
							operator3.Get_suffix());
					String str3 = expression.substring(0,operator1.Get_suffix()+1);
					String str4 = expression.substring(operator3.Get_suffix());
					
					String str = new String();
					
					for(int k = 0;k < str1.length();k++) {
						if(str1.charAt(k) == '(') {
							str1 = str1.substring(k + 1);//消除括号
							k--;
						}
					}
					for(int k = 0;k < str2.length();k++) {
						if(str2.charAt(k) == ')') {
							str2 = str2.substring(0,k);//消除括号
						}
					}
					/*
					System.out.println(expression);
					for(int k = 0;k < suffix.length;k++) {
						System.out.print(suffix[k]);
					}
					System.out.println();
					*/
					for(int k = 1;k < operator3.Get_suffix() - operator1.Get_suffix();k++) {
						if(expression.charAt(k + operator1.Get_suffix()) != 'T') {
							suffix[k + operator1.Get_suffix()] = NO;//修改四元式的结果表示符号的下标数组中的相应元素
						}
					}
					
					//当前要处理的操作符左右两边的数据都为已经处理过的结果
					if(expression.charAt(operator2.Get_suffix() - 1) == 'T' && expression.charAt(operator2.Get_suffix() + 1) == 'T') {
						String string = "("+operator2.Get_op()+","+"T"+suffix[operator2.Get_suffix() - 1]+","+"T"+suffix[operator2.Get_suffix() + 1]+","+"T"+suffix[operator2.Get_suffix()]+")";
						list1.add(string);
						System.out.println(string);
					}
					
					//当前要处理的操作符左边的数据都为已经处理过的结果
					else if(expression.charAt(operator2.Get_suffix() - 1) == 'T') {
						String string = "("+operator2.Get_op()+","+"T"+suffix[operator2.Get_suffix() - 1]+","+str2+","+"T"+suffix[operator2.Get_suffix()]+")";
						list1.add(string);
						System.out.println(string);
					}
					
					//当前要处理的操作符右边的数据都为已经处理过的结果
					else if(expression.charAt(operator2.Get_suffix() + 1) == 'T') {
						String string = "("+operator2.Get_op()+","+str1+","+"T"+suffix[operator2.Get_suffix() + 1]+","+"T"+suffix[operator2.Get_suffix()]+")";
						list1.add(string);
						System.out.println(string);
					}
					
					//当前要处理的操作符左右两边的数据都未被处理过
					else {
						String string = "("+operator2.Get_op()+","+str1+","+str2+","+"T"+NO+")";
						list1.add(string);