Sync with underscore-java.

Author: javadev

checkstyle.xml

@@ -75,7 +75,7 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-checkstyle-plugin</artifactId>
-        <version>2.13</version>
+        <version>2.17</version>
         <executions>
           <execution>
           <id>checkstyle</id>
@@ -160,7 +160,7 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-checkstyle-plugin</artifactId>
-        <version>2.13</version>
+        <version>2.17</version>
         <configuration>
           <configLocation>${basedir}/checkstyle.xml</configLocation>
           <includeTestSourceDirectory>true</includeTestSourceDirectory>

pom.xml

@@ -5,7 +5,7 @@
 import java.util.function.Function;
 
 public abstract class MemoizeFunction<F, T> implements Function<F, T> {
-    private final Map<F, T> cache = new LinkedHashMap<F, T>();
+    private final Map<F, T> cache = new LinkedHashMap<>();
     public abstract T calc(final F n);
 
     public T apply(final F key) {

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

@@ -1,5 +1,6 @@
 package com.github.underscore;
 
+import java.util.Objects;
 import java.util.function.Function;
 import java.util.function.Predicate;
 import java.util.function.Supplier;
@@ -20,16 +21,16 @@ private Optional(final T arg) {
     }
 
     public static <T> Optional<T> of(final T arg) {
-        return new Optional<T>(arg);
+        return new Optional<>(arg);
     }
 
     public static <T> Optional<T> fromNullable(final T nullableReference) {
         return nullableReference == null ? Optional.<T>absent()
-            : new Optional<T>(nullableReference);
+            : new Optional<>(nullableReference);
     }
 
     @SuppressWarnings("unchecked")
-    public static<T> Optional<T> absent() {
+    public static <T> Optional<T> absent() {
         return (Optional<T>) EMPTY;
     }
 
@@ -100,7 +101,7 @@ public boolean equals(final Object o) {
 
         final Optional optional = (Optional) o;
 
-        return absent == optional.absent && !(arg == null ? optional.arg != null : !arg.equals(optional.arg));
+        return absent == optional.absent && Objects.equals(arg, optional.arg);
     }
 
     @Override

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

@@ -11,7 +11,7 @@ public Tuple(final A first, final B second) {
     }
 
     public static <A, B> Tuple<A, B> create(final A a, final B b) {
-        return new Tuple<A, B>(a, b);
+        return new Tuple<>(a, b);
     }
 
     public A fst() {