1. Description
Method reference can be regarded as the deep expression of Lambda expression. In other words, a method reference is a Lambda expression, an example of a functional interface, that points to a method by its name.
2. Usage scenarios
When the operation to be passed to the Lambda body has been implemented, you can use the method reference
3. Format
类(或对象) :: 方法名
4. Example
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)); } }
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