CODEWITHSUNDEEP
javastringloopsfor-loopchar
user1883368
user1883368

Reputation: 71

For loop error, how do i fix this?

for(int x = 0;x<14;x++){
    day[x]= theSheet.changeLetters(day[x]);
}

public String changeLetters(String entering){
    if(entering.equalsIgnoreCase("a")){
        entering = "10";
    } else {
        if(entering.equalsIgnoreCase("b")){
            entering = "11";
        } else {
            if(entering.equalsIgnoreCase("c")){
                entering = "12";
            } else {
                if(entering.equalsIgnoreCase("d")){
                    entering = "13";
                } else {
                    if(entering.equalsIgnoreCase("e")){
                        entering = "14";
                    } else {
                        if(entering.equalsIgnoreCase("f")){
                            entering = "15";
                        } else {
                            if(entering.equalsIgnoreCase("g")){
                                entering = "16";
                            } else {
                                if(entering.equalsIgnoreCase("h")){
                                    entering = "17";
                                }
                            }
                        }
                    }
                }
            }
        }
    }
    return entering;
}

Says the error is here if(entering.equalsIgnoreCase("a")) and in the for loop I am using to run the method. I'm trying to change the letter put into the string into a number.

Can anyone explain to me where the error might be? I'm having trouble spotting the issue. it lets me enter the letters fine but it has an exception once it gets to this for loop and runs this method.

Upvotes: 0

Views: 163

Answers (3)

marc wellman
marc wellman

Reputation: 5886

As @jlordo already stated avoid nested if-statements with such a depth.

As an alternative you might use a switch statement in combination with an enum like this - although the following approach consists of more code it is more general and better suitable to be extended (e.g. using all letter of the alphabet and beyond) and it would make the code much more readable and more appropriate with respect to what you want to express.

Letter letter;

if (letter.equals("a")) letter = Letter.a;
if (letter.equals("A")) letter = Letter.A;
// and so on ...

switch (letter) {
    case a : { 
        // do some code here ...
        break;
    }
    case A : { 
        // do some code here ...
        break;
    }
    // and so on ...
}

public enum Letter {
    a (1),
    A (2),
    b (3),
    B (4),
    c (5),
    C (6);
    // and so on

    private final int index;

    Letter(int i) {

        index = i;
    }

    public int getIndex () {

        return index;
    }
}

Note that if you're using Java 7 you can use the switch statement even without the enum since it accepts strings as well like this:

switch (entering) {

    case "a" : {

        // ...
    }

    // ...
}

Upvotes: 0

Esailija
Esailija

Reputation: 140230

Ok according to

Yes the code is being initialized in a for loop before that one using for(int x =1;x<8;x++){ day[x-1] = JOptionPane.showInputDialog("Enter hour pairs for day "+x +".\n Enter the first digit: "); day[x] = JOptionPane.showInputDialog("Enter the second digit: "); } the letters being put in the array are then changed into numbers using the for loop posted earlier.

You have a logic error. You are overwriting previous entries and not filling the array up to 14 items. So items after 8 are left null, thus the NullPointerException.

Try this:

String[] day = new String[14];

for( int i = 0; i < 14; i+=2 ) {
    day[i] = JOptionPane.showInputDialog("Enter hour pairs for day "+(i/2+1) +".\n Enter the first digit: ");
    day[i+1] = JOptionPane.showInputDialog("Enter the second digit: ");
}

As a bonus, you can simplify the if-else code with:

public String changeLetters( String entering ) {
    return String.valueOf(entering.toUpperCase().charAt(0) - 55);
}

Upvotes: 3

jlordo
jlordo

Reputation: 37813

why don't you use 

if (condition) {
    // ...
} else if (condition2) {
   // ...
} else if (condition3) {
   // ...
}
// and so on

to make your code more readable. Your nested conditions are a mess. If you fix them, you might as well fix the error (if it's in the part of code you showed us).

Also add 

System.out.println("Entering = '" + entering "'");

at the beginnig of your method to see if really receives what you are expecting it to receive.

Upvotes: 4

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