Optional orElse(), orElseGet() and orElseThrow()

spdpiyush · spdpiyush · commit cce9fe7a9ce3 · 2025-03-11T14:17:49.000+05:30
diff --git a/Modern-Java-Examples/src/com/learn/optional/OptionalOrElseExample.java b/Modern-Java-Examples/src/com/learn/optional/OptionalOrElseExample.java
@@ -0,0 +1,68 @@
+package com.learn.optional;
+
+import com.learn.data.Student;
+import com.learn.data.StudentDataBase;
+
+import java.util.Optional;
+
+public class OptionalOrElseExample {
+
+    public static void main(String[] args) {
+
+        System.out.println("Optional orElse() : " + optionalOrElse());
+
+        System.out.println("Optional orElseGet() : " + optionalOrElseGet());
+
+        System.out.println("Optional orElseThrow() : " + optionalOrElseThrow());
+    }
+
+    /**
+     * <p>
+     *     orElse(T) : it accepts the actual value
+     *     If a value is present, returns the value, otherwise returns
+     *     other value passed.
+     * </p>
+     * @return
+     */
+    public static String optionalOrElse() {
+
+        Optional<Student> studentOptional = Optional.ofNullable(StudentDataBase.studentSupplier.get());
+
+        /**
+         * Optional<Student> studentOptional = Optional.ofNullable(null); // it return Optional.empty()
+         * it's going try to map the student object and try to get Name. but since it is empty,
+         * it won't be able to execute map, and execute the orElse and return John.
+         */
+        return studentOptional.map(Student::getName).orElse("John");
+    }
+
+    /**
+     * <p>
+     *     orElseGet(Supplier) : it's going to accept a supplier.
+     *     If a value is present, returns the value, otherwise returns the result
+     *     produced by the supplying function.
+     * </p>
+     * @return
+     */
+    public static String optionalOrElseGet() {
+
+        Optional<Student> studentOptional = Optional.ofNullable(StudentDataBase.studentSupplier.get());
+        return studentOptional.map(Student::getName).orElseGet(() -> "Default");
+    }
+
+    /**
+     * @apiNote
+     * There are 2 different versions of orElseThrow().
+     * <ul>
+     *  <li>orElseThrow() : it throws NoSuchElementException if no value is present </li>
+     *  <li>orElseThrow(Supplier<? extends X> exceptionSupplier) : it accepts exceptionSupplier the
+     *        supplying function that produces an exception to be thrown</li>
+     * </ul>
+     *
+     */
+    public static String optionalOrElseThrow() {
+        Optional<Student> studentOptional = Optional.ofNullable(null);
+        return studentOptional.map(Student::getName)
+                .orElseThrow(() -> new RuntimeException("No Data Found"));
+    }
+}
diff --git a/README.md b/README.md
@@ -58,7 +58,8 @@ This repository contains the basic &amp; advance level examples related to Java
     * [ parallel stream mutating variable](Modern-Java-Examples/src/com/learn/parallelstream/SumClient.java)
   * **Optional** 
     * [Optional Example](Modern-Java-Examples/src/com/learn/optional/OptionalExample.java)
-    * [Optional : ofNullable() , of() , empty()](Modern-Java-Examples/src/com/learn/optional/OptionalOfEmptyNullableExample.java)
+    * [ofNullable(), of() and empty()](Modern-Java-Examples/src/com/learn/optional/OptionalOfEmptyNullableExample.java)
+    * [orElse(), orElseGet() and orElseThrow()](Modern-Java-Examples/src/com/learn/optional/OptionalOrElseExample.java)
 
 <hr />
 
