Java 7 Feature: Asserting Non-Null Objects

Wednesday Mar 30th 2011 by Leonard Anghel
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Java 7 introduces the ability to assert non-null objects. Find out which methods enable this feature and how to use them.

Starting with JDK 7, you can assert non-null objects with two java.util.Objects methods:

  • <T> T nonNull(T obj): This method checks that the specified object reference is not null. It returns obj if the reference is not null, or NullPointerException otherwise.
  • <T> T nonNull(T obj, String message): This method checks that the specified object reference is not null and throws a customized NullPointerException if it is. It returns obj, the object reference to check for nullity, or message, a detailed message to be used in the event that a NullPointerException is thrown.

Here is an example of the two java.util.Objects methods:

package jdk7_nonnull;

import java.util.Objects;

public class Main {

public static void main(String[] args) {

//create a null String object
String nullString = null;
//create a non-null String object
String nonNullString = "Java 7 Rocks!";

//returns nonNullString
String c_nonNullString = Objects.nonNull(nonNullString);
System.out.println(c_nonNullString);

//throw a NullPointerException
String c_nullString_1 = Objects.nonNull(nullString);

//throw a customize NullPointerException
String c_nullString_2 = Objects.nonNull(nullString, "This String is null!");
}
}

Here's the output:

Java 7 Rocks!
Exception in thread "main" java.lang.NullPointerException
at java.util.Objects.nonNull(Objects.java:201)
at jdk7_nonnull.Main.main(Main.java:30)
Java Result: 1
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