How to avoid NullPointerExceptions.

NullPointerExceptions -

1. Call equals() and equalsIgnoreCase() method on known String literal rather unknown object -
   
   Object unknownObject = null;
   
   
   //wrong way - may cause NullPointerException
   if(unknownObject.equals("knownObject")){
      System.err.println("This may result in NullPointerException if unknownObject is null");
   }
   
   
   //right way - avoid NullPointerException even if unknownObject is null
   if("knownObject".equals(unknownObject)){
       System.err.println("better coding avoided NullPointerException");
   }
   
   
2. Prefer valueOf() over toString() where both return same result
   
   BigDecimal bd = getPrice();
   System.out.println(String.valueOf(bd)); //doesn't throw NPE
   System.out.println(bd.toString()); //throws "Exception in thread "main" java.lang.NullPointerException"
3. Using null safe methods and libraries -
   
   //StringUtils methods are null safe, they don't throw NullPointerException
   System.out.println(StringUtils.isEmpty(null));
   System.out.println(StringUtils.isBlank(null));
   System.out.println(StringUtils.isNumeric(null));
   System.out.println(StringUtils.isAllUpperCase(null));
   
   
   Output:
   true
   true
   false
   false
   
   
4. Avoid returning null from method, instead return empty collection or empty array (This Java best practice or tips is also mentioned by Joshua Bloch in his book Effective Java) -
   
   public List getOrders(Customer customer){
      List result = Collections.EMPTY_LIST;
      return result;
   }

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Thanks & Regards
Manish Kumar