[CaptainMorgan]

You titled the thread "recursion", but didn't say whether you wanted to use it and I do not see your attempt at it. You also call a method findLargest, so I don't understand why you need the tester methods. The following compiles and runs - but I'm leaving the findLargest logic up to you - if you get stuck post how you've attempted it. Please use code tags.

Code:

public class ArrayTools {
  double[] doubs = new double[100];
  double maximum;     
  
  public ArrayTools(double[] myArray) {
    this.doubs = myArray;
  }

  public boolean tester() {
    return true;
  }
  
  private boolean tester(double i, int j) {
    return true;
  }

  public double findLargest() {
    // for all values k in doubs, 
    //  iterate over doubs[k], 
    //  compare next value to values already compared
    return maximum;
  }
}

Code:

public class ArrayToolsTest{
  public static void main(String[] args) {
    double[] myArray = { 1.2, 5.7, 4.3, 17.24, 12.34 }; // Fill this array with any doubles
    ArrayTools tester = new ArrayTools(myArray);
    System.out.println("The largest value in the array is " + tester.findLargest());
  }
}