Question

I have created a datatype with two fields, time and measurement. I create an array of these datatypes. When i then attempt to assign a value to one of the fields of array[0] I get a null pointer exception. can anyone tell me what is wrong?

Public class MeasurementPoint{

private int time;
private double  measurement;

public MeasurementPoint(){
this.time =0;
this.measurement =0;}}

public void setMeausurement(double value){
this.measurement = value;}
public double getMeasurement (){
return this.measurement;}

public void setTime(int value){
this.time = value;}
public int getMeasurement (){
return this.time;}
}

The code that I use to create the Array is below

MeasurementPoint [] controlValues = new MeasurementPoint [points];
System.out.println(controlValues.length(); // this gives me 16 so I know the array is created

controlValues[0].setMeasurement(aCtivity);// this is where I get the exception.

Answer 1

You initialized your array but you never initialized your Array Elements, thus you get NullPointerException when you try to acess the zero’th index of your array as yourarray[0] returns null and you try to call setMe…() on null.. you have to actually initialize your array elements.

MeasurementPoint [] controlValues = new MeasurementPoint [points];
controlValues[0] = new Measurementpoint(val1,val2);