Comparator nullsFirst and nullsLast

spdpiyush · spdpiyush · commit 605e484aea71 · 2025-03-13T11:40:05.000+05:30
diff --git a/Modern-Java-Examples/src/com/learn/defaults/DefaultsMethodsExample2.java b/Modern-Java-Examples/src/com/learn/defaults/DefaultsMethodsExample2.java
@@ -27,6 +27,7 @@ public static void main(String[] args) {
 
         comparatorChain(studentList);
 
+        sortWithNullValues(studentList);
     }
 
     public static void sortByName(List<Student> studentList) {
@@ -54,4 +55,27 @@ public static void comparatorChain(List<Student> studentList) {
         studentList.sort(gradeComparator.thenComparing(nameComparator));
         studentList.forEach(studentConsumer);
     }
+
+    /**
+     * If our collection value has null value, but we try to perform sort using comparator.
+     * It will throw NullPointer Exception
+     * To handle these scenarios, Comparator has handy method nulls First and nulls last.
+     */
+    public static void sortCollectionHavingWithNull() {
+        System.out.println("List with Null");
+        List<Student> studentList = StudentDataBase.getAllStudents();
+        studentList.add(null);
+        // comparatorChain(studentList); // throw NPE
+    }
+
+    /**
+     * nullsFirst() : pushes null value at first
+     * nullsLast() : null values will be pushed towards the end.
+     */
+    public static void sortWithNullValues(List<Student> studentList) {
+        studentList.add(null);
+        Comparator<Student> studentComparator = Comparator.nullsFirst(nameComparator);
+        studentList.sort(studentComparator);
+        studentList.forEach(studentConsumer); // prints null first.
+    }
 }
diff --git a/README.md b/README.md
@@ -65,6 +65,7 @@ This repository contains the basic &amp; advance level examples related to Java
   * **Defaults**
     * [default methods](Modern-Java-Examples/src/com/learn/defaults/DefaultsMethodExample.java)
     * [sort using Comparator](Modern-Java-Examples/src/com/learn/defaults/DefaultsMethodsExample2.java)
+    * [Comparator: nullsFirst and nullsLast](Modern-Java-Examples/src/com/learn/defaults/DefaultsMethodsExample2.java)
 
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