CODEWITHSUNDEEP
java
b10hazard
b10hazard

Reputation: 7809

comparison if statment should be called twice but it is only called once when comparing an Integer

I have a function that takes a Integer array and a boolean array. If the value in the Integer array is the highest value and the boolean array is true, the value in the trackerArray is set to true. This is a simplified version of my code that produces the error...

package com.thisis.a.test;

public class ThisIsATest {

    public static void main(String[] args){
        Integer[] integerArray = new Integer[]{75,200,75,200,75};
        boolean[] booleanArray = new boolean[]{false,true,false,true,false};
        boolean[] trackerArray   = new boolean[]{false,false,false,false,false};

        Integer iHighestSum = 0;
        for(int c = 0; c < booleanArray.length; c++){
            if(booleanArray[c] == true)
                if(integerArray[c] > iHighestSum)
                    iHighestSum = integerArray[c];
        }

        for(int c = 0; c < booleanArray.length; c++){
            if(booleanArray[c] == true)
                if(integerArray[c] == iHighestSum) 
                    trackerArray[c] = true; // this if statement should be called twice
        }

        // trackerArray should be {false,true,false,true,false} 
        // instead it is {false,true,false,false,false}
    }
}

The trackerArray should be {false,true,false,true,false}, instead it is {false,true,false,false,false}. The if statment should be triggered twice but instead it is only triggered once. Why is this?

Upvotes: 0

Views: 89

Answers (1)

Bohemian
Bohemian

Reputation: 424993

You should use Integer.equals(), which compares values, not Integer == Integer, which compares object references. Your current code literally says "is the second instance of 200 the same instance as the first instance of 200"

Two options:

  1. Change iHighestSum to int ie int iHighestSum = 0; Java will auto-unbox the Integer to get its int value, then you will be comparing ints, so it's valid to use ==
  2. Change your comparison to use equals(): if(integerArray[c].equals(iHighestSum))

As an interesting side note, your code would pass if you changed the values 200 to 127 (or less). This is because the JVM keeps fixed, reusable Objects inside the Integer class for all values between -128 and 127 (ie a "byte"), ie Integer[] integerArray = new Integer[] { 75, 127, 75, 127, 75 }; passes!

So in summary, either of these changes will make your code function correctly:

...
int iHighestSum = 0;
...
if(integerArray[c].equals(iHighestSum))
...

Upvotes: 5

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