总结自: Java Tips and Best Practices to avoid NPE in Java Applications
- 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");
}
- 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"
- 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
- Avoid returning null from method, instead return empty collection or empty array.
public List getOrders(Customer customer){
List result = Collections.EMPTY_LIST;
return result;
}
- Use of annotation @NotNull and @Nullable
- void unnecessary autoboxing and unboxing in your code
Person ram = new Person("ram");
int phone = ram.getPhone();
- Follow Contract and define reasonable default value
- Use Null Object Pattern
