Check Not Null Precondition 

Google Guava is a java library with lot of utilities and reusable components. This requires the library guava-10.0.jar to be in classpath. The following example shows using Preconditions.checkNotNull() API. It throws NullPointerException if the given reference is null.

File Name  :   com/bethecoder/tutorials/guava/base_tests/CheckNotNullPreTest.java  Author  :   Sudhakar KV Email  :   [email protected]

package com.bethecoder.tutorials.guava.base_tests; import com.google.common.base.Preconditions; public class CheckNotNullPreTest {   /**    * @param args    */   public static void main(String[] args) {     //NullPointerException - if reference is null     //Preconditions.checkNotNull(reference, errorMessage)          /**      * Negative case      */     try {       Preconditions.checkNotNull(System.getProperty("MY_APP_HOME"),          "This program requires MY_APP_HOME system property");     } catch (NullPointerException e) {       System.out.println(e);     }          /**      * Positive case      */     System.setProperty("MY_APP_HOME", "C:\\BTC");     Preconditions.checkNotNull(System.getProperty("MY_APP_HOME"),        "This program requires MY_APP_HOME system property");          System.out.println("Thanks for providing valid input");   } }

java.lang.NullPointerException: This program requires MY_APP_HOME system property
Thanks for providing valid input