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javaif-statementfor-loopincrement
Micah Young
Micah Young

Reputation: 171

Using if else in For Loop increment

I have a problem in Java:

Given a string, return a string made of the chars at indexes 0,1,4,5,8,9...

I know how to solve it, however I was wondering if it's possible for me to use if-else in for-loop increment itself, for example: 

for (int i=0; i < str.length(); if (i%4==0) i++, else i+=3){
    result += str.charAt(i);
}

Can we do something like that?

Upvotes: 15

Views: 7718

Answers (3)

displayName
displayName

Reputation: 14379

Putting it simply, you want two characters from every 4th position starting from 0. You can use the following code for that: 

StringBuilder builder = new StringBuilder();
for (int i = 0; i < safeLength; i += 4){
    builder.Append(str.substring(i, i + 2));
}

Unlike the answer that you have accepted, in this answer there is:

  • no obfuscation;
  • the intent is very clear; and,
  • most importantly, no if-else or ternary operator.

Update: I'm aware of the possibility of IndexOutOfBoundsException but because I wanted to keep the attention on core logic only, I didn't add that check. Here is the code that needs to be added to avoid the exceptional cases:

Put following code above the for loop:

int safeLength = str.Length();
bool lengthCorrectionWasNeeded = (str.length() - 1) % 4 == 0;
if (lengthCorrectionWasNeeded) safeLength--;

Put following code below the for loop:

if (lengthCorrectionWasNeeded) builder.append(str.substring(str.length() - 2));

At the end builder.ToString() will contain the desired string.

Upvotes: 9

Manos Nikolaidis
Manos Nikolaidis

Reputation: 22224

You can't use an if there but you can use a ternary operator

for (int i = 0; i < str.length(); i += i%4 == 0 ? 1 : 3) {
    result += str.charAt(i);
}

Upvotes: 35

Zhli
Zhli

Reputation: 380

As for the issue "Using if else in For Loop increment", I agree with Manos's answer. The following are some of my suggestion. In my opinion, it is important that codes are clear and clean. And it is a good practice that extract str.length() to a local variable instead of 'calculating' it in every loop. And if you are building a string by appending it lots of time, StringBuilder is a good choice.

    String str = "this is your string ...";
    int length = str.length();
    StringBuilder builder = new StringBuilder();
    for (int i = 0; i < length ; i += (i%4 == 0 ? 1 : 3)){
       builder.append(str.charAt(i));
    }
    String result = builder.toString();

Upvotes: 8

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