Question

mainMethod.java

public class mainMethod{
    public animalsData[] animals;

    public mainMethod(){
        animals[this.animals.length + 1] = new animalsData("CAT", "4");

    }

    public static void main(String[] args) {
        mainMethod run = new mainMethod();
    }
}

animalsData.java

public class animalsData{
    String name, l;

    public animalsData(String name, String l) {
        super();
        this.name= name;
        this.l= l;
    }
}

I hava this problem: Exception in thread “main” java.lang.NullPointerException

Answer 1

You are never initializing your animals array in your mainMethod class.

In your public mainMethod() method, you need to do animals = new animalsData[INITIAL SIZE];

If you want it to grow automatically, you should use a List. Even then you would not use this.animals.length + 1 as its index. you would simply do List.add()