Add methods fromNullable(), or() and orNull() for the Optional class.

Author: javadev

src/main/java/com/github/underscore/Optional.java

@@ -1,6 +1,7 @@
 package com.github.underscore;
 
 public final class Optional<T> {
+    private static final Optional<?> EMPTY = new Optional();
     private final T arg;
     private final boolean absent;
 
@@ -9,20 +10,43 @@ private Optional() {
         this.absent = true;
     }
 
-    private Optional(T arg) {
+    private Optional(final T arg) {
         this.arg = arg;
         this.absent = false;
     }
 
-    public static <T> Optional<T> of(T arg) {
+    public static <T> Optional<T> of(final T arg) {
         return new Optional<T>(arg);
     }
 
-    public static <T> Optional<T> absent() {
-        return new Optional<T>();
+    public static <T> Optional<T> fromNullable(final T nullableReference) {
+        return nullableReference == null ? Optional.<T>absent()
+            : new Optional<T>(nullableReference);
+    }
+
+    @SuppressWarnings("unchecked")
+    public static<T> Optional<T> absent() {
+        return (Optional<T>) EMPTY;
     }
 
     public T get() {
+        if (absent) {
+            throw new IllegalStateException("Optional.get() cannot be called on an absent value");
+        }
+        return arg;
+    }
+
+    public T or(final T defaultValue) {
+        if (absent) {
+            return defaultValue;
+        }
+        return arg;
+    }
+
+    public T orNull() {
+        if (absent) {
+            return null;
+        }
         return arg;
     }
 

src/test/java/com/github/underscore/UnderscoreTest.java

@@ -30,6 +30,7 @@
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
 
 /**
  * Underscore library unit test.
@@ -232,6 +233,17 @@ public void optional() {
         assertEquals(Optional.of("123").hashCode(), Optional.of("123").hashCode());
         assertEquals("Optional.absent()", Optional.absent().toString());
         assertEquals("Optional.of(1)", Optional.of(1).toString());
+        assertEquals("Optional.absent()", Optional.fromNullable(null).toString());
+        assertEquals("Optional.of(1)", Optional.fromNullable(1).toString());
+        assertEquals("1", Optional.absent().or(1).toString());
+        assertEquals("1", Optional.of(1).or(2).toString());
+        assertEquals(null, Optional.absent().orNull());
+        assertEquals("1", Optional.of(1).orNull().toString());
+        try {
+            Optional.absent().get();
+            fail("IllegalStateException expected");
+        } catch (IllegalStateException ex) {
+        }
     }
 
     @Test