方法引用

Author: BestBurning

README.md

@@ -38,13 +38,16 @@
 
 - [新的日期时间的API](java-8/src/main/java/com/diyishuai/java8/LocalDateAndTimeAndDateTime.java)
 
-- [默认方法](java-8/src/main/java/com/diyishuai/java8/newinterface)
+- [默认/静态方法](java-8/src/main/java/com/diyishuai/java8/newinterface)
 
-- 方法引用
-
-- 构造器引用
+- [方法引用](java-8/src/main/java/com/diyishuai/java8/function/FunctionReference.java)
 
 - [Optional](java-8/src/main/java/com/diyishuai/java8/optional/OptionalDemo.java)
+
+- JVM的新特性
+
+使用元空间`Metaspace`代替持久代（`PermGen space`），JVM参数使用`-XX:MetaSpaceSize`和`-XX:MaxMetaspaceSize`设置大小
+
 ### JDK 9 
 
 ---

java-8/src/main/java/com/diyishuai/java8/function/FunctionReference.java

@@ -0,0 +1,125 @@
+package com.diyishuai.java8.function;
+
+import lombok.AllArgsConstructor;
+import lombok.Data;
+import lombok.NoArgsConstructor;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.function.BiFunction;
+import java.util.function.Function;
+import java.util.function.Supplier;
+
+/**
+ * @author Shea
+ * @date 2021-01-21
+ * @description
+ */
+public class FunctionReference {
+
+    public static void main(String[] args) {
+        classConstructorFunctionReference();
+        classStaticFunctionReference();
+        instanceFunctionReference();
+    }
+
+
+    /**
+     * 类构造方法引用
+     */
+    private static void classConstructorFunctionReference() {
+        System.out.println("类构造方法引用:");
+        //构造引用
+        // 0 无参构造
+        Supplier<Apple> appleSupplier = Apple::new;
+        Apple a0 = appleSupplier.get();
+        System.out.println(a0);
+        // 1 单参构造
+        Function<String, Apple> appleFunction = Apple::new;
+        Apple a1 = appleFunction.apply("1");
+        System.out.println(a1);
+        // 2 双参构造
+        BiFunction<String, Double, Apple> appleBiFunction = Apple::new;
+        Apple a2 = appleBiFunction.apply("2", 0.5);
+        System.out.println(a2);
+    }
+
+    /**
+     * 类静态方法引用
+     */
+    private static void classStaticFunctionReference() {
+        System.out.println("类静态方法引用");
+        List list = new ArrayList();
+
+        list.add(new Apple("1"));
+        list.add(new Apple("2"));
+        list.add(new Apple("3"));
+        list.add(new Apple[]{new Apple("4"), new Apple("5")});
+
+        list.stream().forEach(Show::show);
+
+    }
+
+
+    /**
+     * 实例方法引用
+     */
+    private static void instanceFunctionReference() {
+        System.out.println("实例方法引用");
+        List<Apple> list = new ArrayList();
+
+        list.add(new Apple("1"));
+        list.add(new Apple("2"));
+        list.add(new Apple("3"));
+
+        list.stream().map(a -> a.getId()).forEach(System.out::println);
+        System.out.println("----");
+        list.stream().map(Apple::getId).forEach(System.out::println);
+    }
+
+
+}
+
+@Data
+@AllArgsConstructor
+@NoArgsConstructor
+class Apple {
+
+    private String id;
+    private double weight;
+    private String color;
+
+    public Apple(String id) {
+        this.id = id;
+    }
+
+    public Apple(String id, double weight) {
+        this.id = id;
+        this.weight = weight;
+    }
+
+    public void show(){
+        System.out.println(this.toString());
+    }
+
+}
+
+class Show {
+
+    public static void show(Object obj) {
+        if (obj instanceof List) {
+            for (Object o : (List) obj) {
+                System.out.print(o.toString() + "\t");
+            }
+            System.out.println();
+        } else if (obj instanceof Object[]) {
+            for (Object o : (Object[]) obj) {
+                System.out.print(o.toString() + "\t");
+            }
+            System.out.println();
+        } else {
+            System.out.println(obj.toString());
+        }
+    }
+
+}