Java Check for Null References

Posted on Apr 17, 2024

In Java we can check for null pointer references using below approaches. If you ask me why we have to do this, is to avoid NullPointerException.

Traditional way

public static List<Integer> getPrices (List<Integer> allPrices) {
    
    if (allPrices == null) {
        return Collections.EMPTY_LIST;
    }

}

Use declarative approach

Before directly jumping into this, I want to share the methods we have to check for null referencs

Objects.isNull()
Objects.nonNull()

These methods we use in functional approach.

import java.util.List;
import java.util.Objects;

public class Sum {
    
    public static Integer getSumOfCollection(List<Integer> num) {
        Integer result = 0 ;
        if (Objects.isNull(num)) {
            return result;
        }
        return num.stream().
        filter(Objects::nonNull).
        mapToInt(Integer::intValue).
        sum();
    }
}

When you call this method with below inputs

 System.out.println(Sum.getSumOfCollection(Arrays.asList(1,2,3,4,5)));
System.out.println(Sum.getSumOfCollection(Arrays.asList(1,null,2,null)));

it will handle the null references gracefully and exclude them.

You can do the same in another approach

return num.stream()
    .filter( eachNum -> eachNum != null)
    .mapToInt(Integer::intValue)
    .sum();

full code used for testing

Main.java

import java.util.Arrays;
import java.util.Optional;

class Main {
    public static void main(String[] args) {
        String name = null;
        try {
            {
                method2();
                throw new NullPointerException("name is null");
            }
        } catch(NullPointerException e) {
            e.printStackTrace();
        } finally {
           
            System.out.println(Sum.getSumOfCollection(Arrays.asList(1,2,3,4,5)));
            System.out.println(Sum.getSumOfCollection(Arrays.asList(1,null,2,null)));

            System.out.println(Sum.getSumOfCollInteger(Arrays.asList(1,2,3,4,5)));
            System.out.println(Sum.getSumOfCollInteger(Arrays.asList(1,null,2,null)));
        }
    }

    public static void method2() {
        String name2 = null;
        Optional<String> optionalStr = Optional.ofNullable(name2); 
        if (!optionalStr.isPresent()) {
            throw new NullPointerException("name2 is null references");
        }
    }
}

Sum.java

import java.util.List;
import java.util.Objects;

public class Sum {
    
    public static Integer getSumOfCollection(List<Integer> num) {
        Integer result = 0 ;
        if (Objects.isNull(num)) {
            return result;
        }
        return num.stream().
        filter(Objects::nonNull).
        mapToInt(Integer::intValue).
        sum();
    }

    public static Integer getSumOfCollInteger(List<Integer> num) {
        Integer result = 0 ;
        if ( Objects.isNull(num)) {
            return result;
        }
        return num.stream()
            .filter(eachInt -> eachInt != null)
            .mapToInt(Integer::intValue)
            .sum();
    }
}

Hope it helps. Thanks.