Java print certain characters from an array

Question

I have a string array that looks like this:

[67, +, 12, -, 45]

I want to print it out so that it looks like this:

67 12 + 45 -

Here's the code I'm trying to use to do this.

String[] temp = line.split(" ");
            String tmp = line.replaceAll("\\s+","");

            for(int i = 0; i < temp.length; i++)
            {
                if(isInt(temp[i]) == false)
                {
                    expression = temp[i];
                    firstExp = true;
                }
                else if(isInt(temp[i]) == false && firstExp == true && secondExp == false)
                {
                    System.out.print(expression);
                    secondExp = true;
                }
                else if(isInt(temp[i]) == false && firstExp == true && secondExp == true)
                {
                    System.out.print(expression);
                    firstExp = false;
                    secondExp = false;
                }
                else
                {
                    System.out.print(temp[i]);
                }
            }

firstExp and secondExp are Booleans that check for the expressions that should appear in the array. isInt() is just a method used to determine if the string is a number. Right now, all this code does is output this:

Basically the rule is that it needs to print all the numbers related to the one expression first, then print the expression itself. — Generalkidd
– Generalkidd, Commented Nov 26, 2013 at 3:51
@JorgeCampos sorry edited...thats what i understand. Please correct if im wrong. — chinna_82
– chinna_82, Commented Nov 26, 2013 at 4:00
How about operator precedence? so [3, +, 4, *, 5] would be: 4 5 * 3 + ? — Dave
– Dave, Commented Nov 26, 2013 at 4:02

Dave · Accepted Answer · 2013-11-26 04:19:17Z

1

public static void main (String[] args) throws java.lang.Exception
    {
        String[] expr = new String[]{"67", "+", "45", "-", "12", "*", "5", "/", "78"};
        int current = 0;
        StringBuilder postfix = new StringBuilder();

        // handle first three
        postfix.append(expr[current]).append(" ");
        postfix.append(expr[current+2]).append(" ");
        postfix.append(expr[current+1]).append(" ");
        current += 3;

        // handle rest
        while( current <= expr.length-2 ){
            postfix.append(expr[current+1]).append(" ");
            postfix.append(expr[current]).append(" ");
            current += 2;
        }

        System.out.println(postfix.toString());
    }

Outputs:

67 45 + 12 - 5 * 78 /

You can run/edit this at: http://ideone.com/zcdlEq

answered Nov 26, 2013 at 4:19

Dave

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Comments

aryann · Accepted Answer · 2013-11-26 04:29:46Z

I guess what you are trying to do is converting infix expression to post fix. Some time back I had written the following code:

    public class InfixToPostfix {
   private Stack stack;
   private String input;
   private String output = "";
   public InfixToPostfix(String in) {
      input = in;
      int stackSize = input.length();
      stack = new Stack(stackSize);
   }
   public String translate() {
      for (int j = 0; j < input.length(); j++) {
         char ch = input.charAt(j);
         switch (ch) {
            case '+': 
            case '-':
            hastOperator(ch, 1); 
            break; 
            case '*': 
            case '/':
            hastOperator(ch, 2); 
            break; 
            case '(': 
            stack.push(ch);
            break;
            case ')': 
            hasSuperior(ch); 
            break;
            default: 
            output = output + ch; 
            break;
         }
      }
      while (!stack.isEmpty()) {
         output = output + stack.pop();
      }
      System.out.println(output);
      return output; 
   }
   public void hastOperator(char op, int precedence) {
      while (!stack.isEmpty()) {
         char opTop = stack.pop();
         if (opTop == '(') {
            stack.push(opTop);
            break;
         }
         else {
            int prec2;
            if (opTop == '+' || opTop == '-')
            prec2 = 1;
            else
            prec2 = 2;
            if (prec2 < precedence) { 
               stack.push(opTop);
               break;
            }
            else
            output = output + opTop;
         }
      }
      stack.push(op);
   }
   public void hasSuperior(char ch){ 
      while (!stack.isEmpty()) {
         char chx = stack.pop();
         if (chx == '(') 
         break; 
         else
         output = output + chx; 
      }
   }
   public static void main(String[] args) 
   throws IOException {
      String input = "67 + 12 - 45";
      String output;
      InfixToPostfix theTrans = new InfixToPostfix(input);
      output = theTrans.translate(); 
      System.out.println("Postfix is " + output + '\n');
   }
   class Stack {
      private int maxSize;
      private char[] stackArray;
      private int top;
      public Stack(int max) {
         maxSize = max;
         stackArray = new char[maxSize];
         top = -1;
      }
      public void push(char j) {
         stackArray[++top] = j;
      }
      public char pop() {
         return stackArray[top--];
      }
      public char peek() {
         return stackArray[top];
      }
      public boolean isEmpty() {
         return (top == -1);
     }
    }
    }

You may need to modify this program to read from an array, but that is very trivial.

Bohemian · Accepted Answer · 2013-11-26 04:54:07Z

1

Here's how you do it in one line:

System.out.println(Arrays.toString(temp).replaceAll("[^\\d +*/-]", "").replaceAll("[+*/-]) (\\d+)", "$2 $1"));

edited Nov 26, 2013 at 4:54

answered Nov 26, 2013 at 4:45

Bohemian♦

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