TokenParser.java

import java.util.ArrayList;
import java.util.List;

/**
 * Created by Lxx on 2017/4/29.
 */
public class TokenParser {
    public List<Token> parse(String expr){
        List<Token> tokens = new ArrayList<>();
        int i = 0;
        while (i < expr.length()) {

            char c = expr.charAt(i);
            if (isOperator(c)) {

                Token t = new Token(Token.OPERATOR,String.valueOf(c));
                tokens.add(t);
                i++;
            }else if(Character.isDigit(c)){
                int nextOperatorIndex = indexOfNextOperator(i,expr);
                String value = expr.substring(i,nextOperatorIndex);
                Token t = new Token(Token.NUMBER,value);
                tokens.add(t);
                i = nextOperatorIndex;
            }else {
                //System.out.println("输入值不符合要求");
                i++;
            }
        }
        return tokens;
    }

    private int indexOfNextOperator(int i, String expr) {
        while(Character.isDigit(expr.charAt(i))){
            i++;
            if(i == expr.length()){
                break;
            }
        }
        return i;
    }

    private boolean isOperator(char c) {
        String sc = String.valueOf(c);
        return Token.OPERATORS.contains(sc);
    }
}