java方法引用是什么

类(或对象) :: 方法名

public class MethodRefTest {

    // 情况一：对象 :: 实例方法

    //Consumer中的void accept(T t)

    //PrintStream中的void println(T t)

    @Test

    public void test1() {

        //使用Lambda表达

        Consumer<String> con1 = str -> System.out.println(str);

        con1.accept("中国");

        System.out.println("====================");

        //使用方法引用

        PrintStream ps = System.out;

        Consumer con2 = ps::println;

        con2.accept("China");

    }

    //Supplier中的T get()

    //Employee中的String getName()

    @Test

    public void test2() {

        //使用Lambda表达

        Employee emp = new Employee(1001, "Bruce", 34, 600);

        Supplier<String> sup1 = () -> emp.getName();

        System.out.println(sup1.get());

        System.out.println("====================");

        //使用方法引用

        Supplier sup2 = emp::getName;

        System.out.println(sup2.get());

    }

    // 情况二：类 :: 静态方法

    //Comparator中的int compare(T t1,T t2)

    //Integer中的int compare(T t1,T t2)

    @Test

    public void test3() {

        //使用Lambda表达

        Comparator<Integer> com1 = (t1, t2) -> Integer.compare(t1, t2);

        System.out.println(com1.compare(32, 45));

        System.out.println("====================");

        //使用方法引用

        Comparator<Integer> com2 = Integer::compareTo;

        System.out.println(com2.compare(43, 34));

    }

    //Function中的R apply(T t)

    //Math中的Long round(Double d)

    @Test

    public void test4() {

        //使用匿名内部类

        Function<Double, Long> func = new Function<Double, Long>() {

            @Override

            public Long apply(Double aDouble) {

                return Math.round(aDouble);

            }

        };

        System.out.println(func.apply(10.5));

        System.out.println("====================");

        //使用Lambda表达式

        Function<Double, Long> func1 = d -> Math.round(d);

        System.out.println(func1.apply(12.3));

        System.out.println("====================");

        //使用方法引用

        Function<Double, Long> func2 = Math::round;

        System.out.println(func2.apply(12.6));

    }

    // 情况三：类 :: 实例方法

    // Comparator中的int comapre(T t1,T t2)

    // String中的int t1.compareTo(t2)

    @Test

    public void test5() {

        //使用Lambda表达式

        Comparator<String> com1 = (s1, s2) -> s1.compareTo(s2);

        System.out.println(com1.compare("abd", "aba"));

        System.out.println("====================");

        //使用方法引用

        Comparator<String> com2 = String::compareTo;

        System.out.println(com2.compare("abd", "abc"));

    }

    //BiPredicate中的boolean test(T t1, T t2);

    //String中的boolean t1.equals(t2)

    @Test

    public void test6() {

        //使用Lambda表达式

        BiPredicate<String, String> pre1 = (s1, s2) -> s1.equals(s2);

        System.out.println(pre1.test("abc", "abc"));

        System.out.println("====================");

        //使用方法引用

        BiPredicate<String, String> pre2 = String::equals;

        System.out.println(pre2.test("abc", "abd"));

    }

    // Function中的R apply(T t)

    // Employee中的String getName();

    @Test

    public void test7() {

        //使用Lambda表达式

        Employee employee = new Employee(1001, "Tom", 45, 10000);

        Function<Employee, String> func1 =e->e.getName();

        System.out.println(func1.apply(employee));

        System.out.println("====================");

        //使用方法引用

        Function<Employee,String>func2 = Employee::getName;

        System.out.println(func2.apply(employee));

    }

}