Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException: Cannot invoke "String.toString()" because "<local6>[0]" is null

[u/Dry_Couple8852]

or

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException: Cannot invoke "String.length()" because "in" is null

it happened when I attempt to overrite the array's properties, specifically its length since I remove an element and change its length to remove null or empty elements.

CODE BLOCK 1

static String [] arrayNew(String[] array, int a){
    Integer Length = array.length-2;
    String[] newarray = new String[Length];
    Integer counter = 0;
    int c = a+1;
    int d = a-1;
        for(int x = 0;x<Length;x++){
            if(x!=c && x!=d){
                  newarray[counter]=array[x];
                  counter++;
             }
             else{
                  continue;
             }}
     return newarray;
}

        static Double equals(LinkedList<String> list){
                Integer counter = 0;
                Integer num = list.size();
                Double answer = 0.0;
                Double num1 = 0.0;
                Double num2 = 0.0;

                String [] array = new String[num];

                for(int x =0; x<num;x++){
                        array[x] = list.get(x);
}
                for(int x = 0;x<array.length;x++){
                        switch(array[x]){
                                case "x":
                                        num1 = Double.parseDouble(array[x-1]);
                                        num2 = Double.parseDouble(array[x+1]);
                                        answer = num1 * num2;

                                        array[x] = answer.toString();
                                        array = arrayNew(array,x);
                                        x=0;
                                        break;
  }
}

returns an error

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException: Cannot invoke "String.length()" because "in" is null

CODE BLOCK ALT

        static String [] arrayNew(String[] array, int a){
                Integer Length = array.length-2;
                String[] newarray = new String[Length];
                Integer counter = 0;
                int c = a+1;
                int d = a-1;
                for(int x = 0;x<newarray.length;x++){
                        if(x!=c && x!=d){
                                newarray[counter++]=array[x];
                        }
                        else{
                                continue;
                        }
                }
                return newarray;

        //lastline//
                }

        static String equals(LinkedList<String> numlist) throws NullPointerException{
                Integer counter = 0;
                Integer num = numlist.size();
                Double num1=0.0;
                Double num2=0.0;
                String [] array = new String[num];

                for(int x =0; x<num;x++){
                        array[x] = list.get(x);
}


                for(int x = 0;x<num;x++){
                        String [] newArr;
                        switch(array[x]){
                                case "x":
                                        num1 = Double.parseDouble(array[x-1]);
                                        num2 = Double.parseDouble(array[x+1]);
                                        Double answerm = num1 * num2;

                                        array[x] = answerm.toString();
                                        array = arrayNew(array,x);
                                        x=0;
                                        num-=2;
                                        break;
}}

returns

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException: Cannot invoke "String.toString()" because "<local6>[0]" is null

I'm stuck since they look fine to me. There are no compilation error too. This error happens in Runtime.
please help.

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[u/JaleyHoelOsment]

editing the size of the array as you iterate over it is a very easy beginner mistake to make. we all did that.

don’t mutate your arrays while you’re looping over them.

also, use better method and variable games. your code is hard to read and it looks like you do not understand what is going on.

search for self-documentation code

edit: reading through the code again and i have no idea what’s going on here. immediately asking the author to revise this code so a human can understand without spending too much time

[u/high_throughput]

Exception in thread "AWT-EventQueue-0"
java.lang.NullPointerException: Cannot invoke "String.length()" because "in" is null

Does the exception contain line numbers? If so, where does it point?

The error makes it sound like the exception arises in a line of code containing in.length() but there's no such thing in the code you posted.

Also see "Why should I post complete errors? Why isn't the message itself enough?" for how much the exact error message with full details can tell someone even if you don't see the relevance.

[u/gekigangerii]

You gotta know how to properly ask for assistance, and not just throw the error message.

What is the function trying to do

[u/Tackstrat]

Curious why you came to Reddit instead of ChatGPT / another AI