使用Stream对map排序

Author: MyHerux

src/main/java/com/xu/java8/Optional/Optional1.java

@@ -33,6 +33,8 @@ public static void main(String[] args) {
         System.out.println(optional.orElse("fallback"));
         optional.ifPresent(System.out::println);
         optional2.ifPresent(System.out::println);
+
+        System.out.println(Optional.ofNullable(null).isPresent());
     }
 }
 

src/main/java/com/xu/java8/Stream/Streams1.java

@@ -1,8 +1,6 @@
 package com.xu.java8.Stream;
 
-import java.util.ArrayList;
-import java.util.List;
-import java.util.Optional;
+import java.util.*;
 
 /**
  * Class java8-Stream接口

src/main/java/com/xu/java8/Stream/Streams6.java

@@ -0,0 +1,38 @@
+package com.xu.java8.Stream;
+
+import java.util.HashMap;
+import java.util.LinkedHashMap;
+import java.util.Map;
+
+/**
+ * Created by xu on 2016/9/13.
+ */
+public class Streams6 {
+    public static void main(String args[]) {
+        Map<String, Integer> unsortMap = new HashMap<>();
+        unsortMap.put("z", 10);
+        unsortMap.put("b", 5);
+        unsortMap.put("a", 6);
+        unsortMap.put("c", 20);
+        unsortMap.put("d", 1);
+        unsortMap.put("e", 7);
+        unsortMap.put("y", 8);
+        unsortMap.put("n", 99);
+        unsortMap.put("j", 50);
+        unsortMap.put("m", 2);
+        unsortMap.put("f", 9);
+        System.out.println(sortByValue(unsortMap));
+    }
+
+    /**
+     * 使用stream类来对map的value排序(并行排序,逆序)
+     */
+    public static <K, V extends Comparable<? super V>> Map<K, V>
+    sortByValue(Map<K, V> map) {
+        Map<K, V> result = new LinkedHashMap<>();
+        map.entrySet().parallelStream().sorted((o1, o2) -> (o2.getValue()).compareTo(o1.getValue())).forEachOrdered(x ->
+                result.put(x.getKey(), x
+                        .getValue()));
+        return result;
+    }
+}