Question

I have created a method which takes generate random numbers with the condition that the next random number doesn’t match with the previous one inside the array here’s the code

// some code   

int k=0;

//some code....

randomgenerator(k); // method call

public void randomgenerator(int j)
{

    for(j=0; j<=99; j++){
        if(j >= 1){
            if (randomset.get(j) == randomset.get(j-1)){
                randomset.add(0 + ( j  ,  int)(Math.random() * ((99 - 0) + 1)));
            }
            else{
                randomset.add(0 + (int)(Math.random() * ((99 - 0) + 1)));
            }
        }       
    }
}

The error I get is java.lang.IndexOutOfBoundsException: Invalid index 1, size is 1

Answer 1

Because initially randomset is empty therefore its size is 0 and returns exception at index 1. The best way to add randomset.add(0 + (int)(Math.random() * ((99 - 0) + 1))); if j < 1 (not >=1).

Correct code:

public void randomgenerator(int j)
{
for(j=0; j<=99; j++){
    if(j >= 1){
        if (randomset.get(j) == randomset.get(j-1)){
            randomset.add(0 + ( j  ,  int)(Math.random() * ((99 - 0) + 1)));
        }
        else{
            randomset.add(0 + (int)(Math.random() * ((99 - 0) + 1)));
        }
    }
    else {
           randomset.add(0 + (int)(Math.random() * ((99 - 0) + 1)));
    }       
}

}