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Calc.java
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Calc.java
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/**
* @author kunpeng
* 计算器
*/
public class Calc {
/**
* @param args
*/
public static void main(String[] args) {
String source = " ( 1 + 5 * ( 20 + 1 ) + 1 ) * 10 ";
Parser parser = new Parser();
Node root = parser.parse(source);
int result = root.exec();
System.out.println(source+"="+result);
}
public static class Parser{
private Scanner fScanner;
private Token token;
public Node parse(String source){
fScanner = new Scanner(source);
advance();
Node opNode = matchOpExpr();
return opNode;
}
private Node matchOpExpr() {
switch (token.type) {
case '(':{
GroupNode gNode = matchGroup();
advance();
if(token.type == Scanner.OP){
return matchOpExpr(gNode);
}else if(token.type == Scanner.EOF){
return gNode;
}
}
break;
case Scanner.NUM:{
Token num1 = token;
NumberNode lhs = new NumberNode();
lhs.value = num1.value;
advance();
if(token.type == Scanner.OP){
return matchOpExpr(lhs);
}else if(token.type == Scanner.EOF){
return lhs;
}
}
default:
System.err.println("error");
break;
}
return null;
}
private GroupNode matchGroup() {
advance();
GroupNode gNode = new GroupNode();
gNode.expr = matchOpExpr();
if(token.type!=')'){
System.err.println("expected ')' but '"+token.value+"'");
}
return gNode;
}
public OpNode matchOpExpr(Node lhs) {
OpNode opNode = new OpNode();
Token op = token;
advance();
Node rhs = null;
if(token.type == '('){
rhs = matchGroup();
}else{
Token num2 = token;
NumberNode rhs1 = new NumberNode();
rhs1.value = num2.value;
rhs = rhs1;
}
advance();
opNode.left = lhs;
opNode.right = rhs;
opNode.op = (char) op.value.charAt(0);
if(token.type==Scanner.OP){
if(token.priority > op.priority){
opNode.right = matchOpExpr(rhs);
}else{
opNode = matchOpExpr(opNode);
}
}
return opNode;
}
private void advance() {
token = fScanner.nextToken();
}
}
public static class Scanner{
public String fSource;
private int index = 0;
private int start = 0;
public static final int NUM = 0;
public static final int OP = 1;
public static final int EOF = -1;
public Scanner(String source){
fSource = source;
}
private void advance(){
index++;
}
private boolean isEOF(){
return index >= fSource.length();
}
public Token nextToken(){
start = index;
Token token = new Token();
if(isEOF()){
token.type = EOF;
return token;
}
char ch = fSource.charAt(index);
advance();
switch (ch) {
case '0':
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
case '8':
case '9':
while(!isEOF() && Character.isDigit(fSource.charAt(index))){
advance();
}
token.type = NUM;
token.value = fSource.substring(start, index);
break;
case '(':
case ')':
token.type = ch;
token.value = String.valueOf(ch);
break;
case '+':
case '-':
token.priority = 1;
token.type = OP;
token.value = String.valueOf(ch);
break;
case '*':
case '/':
token.priority = 2;
token.type = OP;
token.value = String.valueOf(ch);
break;
case ' ':
token = nextToken();
break;
default:
System.err.println("error code : "+ch);
break;
}
return token;
}
}
public static class Token{
public int type;
public short priority;
public String value;
@Override
public String toString() {
return "Token [type=" + type + ", value=" + value + "]";
}
}
public static class Node{
public int exec() {
return -1;
}
}
public static class NumberNode extends Node{
String value;
@Override
public int exec() {
return Integer.parseInt(value);
}
}
public static class GroupNode extends Node{
public Node expr;
@Override
public int exec() {
return expr.exec();
}
}
public static class OpNode extends Node{
public char op;
public Node left;
public Node right;
public int exec() {
switch (op) {
case '+':
return left.exec() + right.exec();
case '-':
return left.exec() - right.exec();
case '*':
return left.exec() * right.exec();
case '/':
return left.exec() / right.exec();
default:
break;
}
return super.exec();
}
}
}