How to Sort object property with null values using Java 8 Lambda expression

Sort custom object property with null values using Java 8 lambda expression

What is lambda expression?

The expression through which we can represent an anonymous function.

learn more about lambda expression :

• Lambda Expression in Java 8 with examples  

Lets see how we can sort custom object property without and with lambda expression.

Example 1 : Sort custom object without lambda expression using Collections.sort()

Programming.java

public class Programming {

    private int id;
    private String name;
    
    public Programming(int id, String name) {
        this.id = id;
        this.name = name;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    @Override
    public String toString() {
        return "Programming [id = " + id + ", name = " + name + "]";
    }
    
}

SortObjectPropertyByLambda.java

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class SortObjectPropertyByLambda {

    public static void main(String[] args) {
       
        List<Programming> language = new ArrayList<Programming>() {{
            add(new Programming(1, "Java"));
            add(new Programming(2, "Python"));
            add(new Programming(5, "JavaScript"));
            add(new Programming(10, "Php"));
            add(new Programming(4, "Dotnet"));
            add(new Programming(20, "ReactNative"));
            add(new Programming(6, "AngularJs"));
        }};
       
        Comparator<Programming> comparator = new Comparator<Programming>() {
           
            @Override
            public int compare(Programming o1, Programming o2) {
                return o1.getName().compareTo(o2.getName());
            }
        };
       
        Collections.sort(language, comparator);
        System.out.println(language);
       
    }
}

Output :

[Programming [id = 6, name = AngularJs],
Programming [id = 4, name = Dotnet],
Programming [id = 1, name = Java],
Programming [id = 5, name = JavaScript],
Programming [id = 10, name = Php],
Programming [id = 2, name = Python],
Programming [id = 20, name = ReactNative]]

For reverse order, change in return statement in compare method like below :

public int compare(Programming o1, Programming o2) {
     return o2.getName().compareTo(o1.getName());
}

Example 2 : Sort custom object with Java 8 lambda expression using Collections.sort()

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class SortObjectPropertyByLambda {

    public static void main(String[] args) {
       
        List<Programming> language = new ArrayList<Programming>() {{
            add(new Programming(1, "Java"));
            add(new Programming(2, "Python"));
            add(new Programming(5, "JavaScript"));
            add(new Programming(10, "Php"));
            add(new Programming(4, "Dotnet"));
            add(new Programming(20, "ReactNative"));
            add(new Programming(6, "AngularJs"));
        }};
       
        Collections.sort(language, (o1, o2) -> o1.getName().compareTo(o2.getName()));
        System.out.println(language);
    }
    
}

If we try to sort object with null value, then we get following exception.

Exception in thread "main" java.lang.NullPointerException
    at Java8.SortObjectPropertyByLambda.lambda$0(SortObjectPropertyByLambda.java:23)

So we can use Comparator comparing method for sort null value as well. lets see example for that.

Example 3 : Sort custom object property with null values in java

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class SortObjectPropertyByLambda {

    public static void main(String[] args) {
       
        List<Programming> language = new ArrayList<Programming>() {{
            add(new Programming(15, "null"));
            add(new Programming(1, "Java"));
            add(new Programming(2, "Python"));
            add(new Programming(5, "JavaScript"));
            add(new Programming(10, "Php"));
            add(new Programming(4, "Dotnet"));
            add(new Programming(20, "ReactNative"));
            add(new Programming(6, "AngularJs"));
            add(new Programming(6, "null"));
           
        }};
       
        Comparator<Programming> comparator = Comparator.comparing(Programming::getName,
                Comparator.nullsLast(Comparator.naturalOrder())
        );
       
        Collections.sort(language, comparator);
        System.out.println(language);
    }
}

Output :

[Programming [id = 6, name = AngularJs],
Programming [id = 4, name = Dotnet],
Programming [id = 1, name = Java],
Programming [id = 5, name = JavaScript],
Programming [id = 10, name = Php],
Programming [id = 2, name = Python],
Programming [id = 20, name = ReactNative],
Programming [id = 15, name = null],
Programming [id = 6, name = null]]

We can also reverse the data using Comparator.reverseOrder() method.

Other related articles :

• Sort java List by Object property with null check using Comparator
• Comparable Interface in Java with Examples