how to concatenate tokens and strings and numbers in java?

Question

I have a program where I'm trying to concatenate token objects with string, using operands (numbers and variables) and operators (+, -, *, /):

         private static Token evalOp(Token op, Token t1, Token t2) { 
             return "Operator: [" + op + "]; Operand1: [" + t1 +"]; Operand2 [" + t2 + "]";

}

I have a separate array of tokens, that I'm trying to add onto.

  private static ArrayList<Token> infixToPostfix(ArrayList<Token> intokens) {
      String string = "";
      Stack s = new Stack();
      for (int i = 0; i < s.length(); i++){
         if (intokens[i]==operand){
            string+=intokens[i];
         }
         else if (intokens[i]==operator){
            while (!s.empty()/*&&hasHigherPrecedence(s.top(), intokens[i])*/){
                string+=s.pop();
               s.pop();
            }
             s.push(intokens[i]);
         }
      }
   }

Its for an infix to postfix program. I want to convert infix to postfix and display it in an array. I originally thought the problem had to do with concatenating strings and numbers, but I now believe I was wrong. You'll notice the first code was just replaced. That's because the old code had several if-statements that concatenated numbers and tokens. The tokens could be numbers or variables. I sort of forgot and made the stupid mistake treating it above like they were numbers.

Anyways, I want the user to enter an infix expression, like

2 * 3 + 5

and convert it to

2 3 * 5 +

See what I mean? It takes in an expression, then it returns it as a postfix expression. But the postfix expression needs to have these types of strings around it, so the output would really be:

[num: 2], [num: 3], [op: *], [num: 5], [op: +]

See what I mean? I also have another function in my code, in addition to the main method for making an arrayList of token:

private static ArrayList<Token> parse(String s) {
  // make a loop and take each char out of the String s, one by one and check
  //   to see what token type it is. Then store the token type in an ArrayList of tokens
  for (int i = 0; i < s.length(); i++){
     char c = s.charAt(i);
     String v = Character.toString(c);
     TokenType t = getTokenType(c);
     if (t==null){
        //print error
        System.out.println("Error");
     }
     else if(!t.equals(TokenType.WS)){
        //add to array
        list.add(TokenType.WS);
     }
  }
  return list;
   }

I have more code, but basically, I want to convert infix to postfix and I want to evaluate it. It has to pass this algorithm as a test:

class SimpleCalcTest {

public static void test() {
    String[] inputs = {
        "3*4 + 5",
        "3 + 4*5",
        "(1+1)*(5-2)",
        "(3*4+5)*(3*3 + 4*4)"
    };

    for (int i=0; i<inputs.length; i++) {
        String s = inputs[i];
        System.out.println();
        System.out.println();
        System.out.println("test:  input = " + s);
        String r = SimpleCalc.evalExpression(s);
        System.out.println("\tresult = " + r);
    }
}


public static void main(String[] args) {
    SimpleCalc.commandLine();
}

This code compiles and executes. What's the problem? – user207421 Oct 12 '15 at 02:09 — user207421, Oct 12 '15 at 02:09

score 0 · Answer 1 · answered Oct 11 '15 at 23:10

0

You can. You're doing something else wrong but you haven't given enough context. The following works so compare it with your own code:

class Foo {
    public static void main(String[] args) {
        System.out.println(demo());
    }

    static String demo() {
        int t1 = 5;
        int t2 = 3;
        return "Answer: " + (t1 - t2);
    }
}

$ java -version
java version "1.7.0_79"
OpenJDK Runtime Environment (IcedTea 2.5.6) (7u79-2.5.6-0ubuntu1.14.04.1)
OpenJDK 64-Bit Server VM (build 24.79-b02, mixed mode)
$ javac Foo.java
$ java Foo
Answer: 2

answered Oct 11 '15 at 23:10

BaseZen

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Ok, I'll add in some more of my code then, because its a lot longer. Tell me if I'm adding too much. – user3363511 Oct 11 '15 at 23:18
I was wrong. I asked the wrong question. I thought my error had to do with concatenating tokens (which could sometimes be numbers), and I was wrong. I see the flaws in my logic now. I should have asked this more directly. – user3363511 Oct 12 '15 at 05:02

how to concatenate tokens and strings and numbers in java?

1 Answers1