019_JDK8.0新特性<三>函数引用_构造器引用_数组引用

1. 函数引用 :

• 若Lambda体中的内容已经有方法实现过了,则可以使用"方法引用"
• 函数引用可以理解为Lambda表达式的另一种表现形式

2. 语法格式

• 注意 : 

  • Lambda体中调用方法的参数列表与返回值类型,须与函数式接口中抽象方法的参数列表和返回值类型一直.
  • 当Lambda参数列表中,第一个参数是实例函数的调用者,而第二个参数是实例函数的形式参数时,可以是用          类名::实例函数名      的形式.

• 对象名 ::实力函数名

    @Test
    public void test1() {
        //  对象::实例方法名
        //  输出任意内容
        PrintStream ps = System.out ;
        Consumer<String> consumer = (x) ->ps.println(x);
        consumer.accept("业精于勤荒于嬉,行成于思毁于随");

        PrintStream ps1 = System.out ;
        Consumer<String> consumer1 = ps1::println ;
        consumer1.accept("马云传：未来的你，一定会感谢今天拼命努力的自己!");
        //  函数接口的泛型在控制数据类型
        Consumer<Integer> consumer2 = System.out::println;
        consumer2.accept(9527);
    }

• 类名::静态方法名

    @Test
    public void test3() {
        //  类名::静态函数
        //  编写比较器
        Comparator<Integer> comparator = (x, y) -> Integer.compare(x, y);

        Comparator<Integer> comparator1 = Integer::compare ;

        int compare = comparator1.compare(120, 120);
        System.out.println("compare = " + compare);
    }

• 类名::函数名

    @Test
    public void test4() {
        //  类名::函数名
        //  比较两个字符串
        //  方法一 : BiPredicate
        BiPredicate<String,String> biPredicate = (x,y)->x.equals(y) ;
        System.out.println("biPredicate.test("abc","abc") = " + biPredicate.test("abc", "abc"));
        BiPredicate<String,String> biPredicate1 = String :: equals ;
        System.out.println(biPredicate1.test("郭靖","郭靖"));

        //  方法二 : BiFunction
        BiFunction<String,String,Boolean> function = (x, y) -> x.equals(y);
        Boolean apply = function.apply("abc", "abc");
        System.out.println("apply = " + apply);

        BiFunction<String,String,Boolean> function1 = String::equals ;
        System.out.println("function1.apply("abc","abc") = " + function1.apply("abc", "abc"));
    }

3. 构造器引用

• 格式 :    classname::new

    @Test
    public void test01() {
        //  构造器引用
        Employee employee = new Employee();

        Supplier<Employee> supplier = Employee::new ;
        Employee employee1 = supplier.get();
        System.out.println("employee1 = " + employee1);
        //  一个参数
        Function<String,Employee> function = Employee::new ;
        Employee employee2 = function.apply("xiaoixao");
        System.out.println("employee2 = " + employee2);
        //  二个参数
        BiFunction<String,Integer,Employee> biFunction = Employee::new ;
        Employee employee3 = biFunction.apply("xiaoxiao", 30);
        System.out.println("employee3 = " + employee3);
    }

4. 数组引用

• 格式 : 数据类型[]::new

    @Test
    public  void test02() {
        //
        int[] arr = new int[10] ;

        Function<Integer,int[]> function = int[]::new ;
        int[] ints = function.apply(10);
        System.out.println("ints = " + ints);
        Function<Integer,Employee[]> function1 = Employee[]::new ;

        Employee[] employees = function1.apply(100);
        System.out.println(Arrays.toString(employees));

        Function<Object[],String> function2 = employees1->Arrays.toString(employees1);
        String apply = function2.apply(employees);
        System.out.println("apply = " + apply);
    }