[Q#425439][A#425466] How to check if array element is null to avoid NullPointerException in Java

https://stackoverflow.com/q/425439

I have a partially nfilled array of objects, and when I iterate through them I tried to check to see whether the selected object is null before I do other stuff with it. However, even the act of checking if it is null seem to through a NullPointerException. array.length will include all null elements as well. How do you go about checking for null elements in an array? For example in the following code will throw an NPE for me.

Answer

https://stackoverflow.com/a/425466

You have more going on than you said. I ran the following expanded test from your example: and got the expected output: Are you possibly trying to check the lengths of someArray[index]?

APIzation

public class test {

    public static void main(String[] args) {
        Object[][] someArray = new Object[5][];
        someArray[0] = new Object[10];
        someArray[1] = null;
        someArray[2] = new Object[1];
        someArray[3] = null;
        someArray[4] = new Object[5];

        for (int i=0; i<=someArray.length-1; i++) {
            if (someArray[i] != null) {
                System.out.println("not null");
            } else {
                System.out.println("null");
            }
        }
    }
}
$ /cygdrive/c/Program\ Files/Java/jdk1.6.0_03/bin/java -cp . test
not null
null
not null
null
not null

package com.stackoverflow.api;

public class Human425466 {

  public static void checkIfElementIsNull(Object[][] someArray) {
    for (int i = 0; i <= someArray.length - 1; i++) {
      if (someArray[i] != null) {
        System.out.println("not null");
      } else {
        System.out.println("null");
      }
    }
  }
}

package com.stackoverflow.api;

/**
 * How to check if array element is null to avoid NullPointerException in Java
 *
 * @author APIzator
 * @see <a href="https://stackoverflow.com/a/425466">https://stackoverflow.com/a/425466</a>
 */
public class APIzator425466 {

  public static void check(Object[][] someArray) {
    for (int i = 0; i <= someArray.length - 1; i++) {
      if (someArray[i] != null) {
        System.out.println("not null");
      } else {
        System.out.println("null");
      }
    }
  }
}