import java.util.HashMap;
public class OperatorPrioritySaver {
HashMap priorityMap = new HashMap();
public OperatorPrioritySaver() {
priorityMap.put("+", 1);
priorityMap.put("-", 1);
priorityMap.put("*", 2);
priorityMap.put("/", 2);
priorityMap.put("%", 2);
}
int comp(String op1, String op2) throws RuntimeException{
if(priorityMap.get(op1)==null ){
throw new RuntimeException("not an accept op :" +op1);
}
if(priorityMap.get(op2)==null ){
throw new RuntimeException("not an accept op :" +op2);
}
return priorityMap.get(op1).compareTo(priorityMap.get(op2));
}
boolean acceptOperator(String test){
return priorityMap.keySet().contains(test);
}
}
import java.util.Stack;
public class ExpressionParser {
private String exprString ;
private int value ;
OperatorPrioritySaver opsvr = new OperatorPrioritySaver();
Stack nums = new Stack();
Stack ops = new Stack();
public ExpressionParser(String exprString) {
this.exprString = exprString ;
}
public String getExprString(){
return exprString ;
}
public int getValue() {
return value;
}
public String toString() {
return exprString +" = " + value ;
}
public void parse() {
String terns[] = exprStr2Terns();
int num = 0 ;
String op = null ;
for(String tern : terns){
try{
num = Integer.parseInt(tern) ;
op = null ;
}catch(NumberFormatException e){
op = tern ;
}
if(op == null){ // number
nums.push(num);
}else{ // operator
String top = null ;
if("(".equals(op) || ")".equals(op)){
if("(".equals(op)){
ops.push(op);
}else if(")".equals(op)){
while( (top = ops.pop()) != null &&
(!top.equals("("))){
doOperator(top);
}
}
}else if(opsvr.acceptOperator(op)){
while( ops.size() > 0 &&
(top = ops.peek()) != null &&
(!top.equals("(")) &&
(opsvr.comp(top, op)>=0)){
top = ops.pop();
doOperator(top);
}
ops.push(op);
}else {
System.err.println("Unsupported operator : " + op);
}
}
}
while(ops.size() != 0){
doOperator(ops.pop());
}
value = nums.get(0);
}
private String[] exprStr2Terns() {
// 目前使用空格隔開所有的符號
// 想不用空格隔開 可以自行修改
return exprString.split(" ");
}
private void doOperator(String op) {
char opCh = op.toCharArray()[0];
int num2 = 0, num1 = 0;
switch(opCh){
case '+':
num2 = nums.pop();
num1 = nums.pop();
nums.push(num1+num2);
break;
case '-':
num2 = nums.pop();
num1 = nums.pop();
nums.push(num1-num2);
break;
case '*':
num2 = nums.pop();
num1 = nums.pop();
nums.push(num1*num2);
break;
case '/':
num2 = nums.pop();
num1 = nums.pop();
nums.push(num1/num2);
break;
case '%':
num2 = nums.pop();
num1 = nums.pop();
nums.push(num1%num2);
break;
}
}
public static void main(String[] args) {
ExpressionParser expr = new ExpressionParser("( 1 + 2 ) * 3");
expr.parse();
System.out.println(expr);
}
}
