1. 方法引用介绍
方法引用其实是lambda表达式的升级写法,采用::
固定语法,可以使代码更简洁、紧凑;
2. 方法引用的5种类型
2.1 对象引用::实例方法名
函数式接口抽象方法的形参列表与实例方法的一致,且方法的返回值类型一致;
public class MethodReferencesTest {
public static void main(String[] args) {
// 对象引用
MethodReferencesTest methodReferencesTest = new MethodReferencesTest();
// lambda表达式写法
Integer r1 = MethodReferencesTest.getResult((a, b) -> methodReferencesTest.sum(a, b));
System.out.println("r1:" + r1);
// 方法引用(对象引用::实例方法名)写法
Integer r2 = MethodReferencesTest.getResult(methodReferencesTest::sum);
System.out.println("r2:" + r2);
}
public static Integer getResult(CalculateInterface calculateInterface) {
return calculateInterface.calculate(123, 456);
}
/**
* 实例方法
*/
public Integer sum(Integer a, Integer b) {
return a + b;
}
}
@FunctionalInterface
interface CalculateInterface {
/**
* 函数式接口抽象方法
*/
Integer calculate(Integer a, Integer b);
}
// 运行结果
r1:579
r2:579
2.2 类名::静态方法名
函数式接口抽象方法的形参列表与静态方法的一致,且方法的返回值类型一致;
public class MethodReferencesTest {
public static void main(String[] args) {
// lambda表达式写法
Integer r1 = MethodReferencesTest.getResult((a, b) -> MethodReferencesTest.sum(a, b));
System.out.println("r1:" + r1);
// 方法引用(类名::静态方法名)写法
Integer r2 = MethodReferencesTest.getResult(MethodReferencesTest::sum);
System.out.println("r2:" + r2);
}
public static Integer getResult(CalculateInterface calculateInterface) {
return calculateInterface.calculate(123, 456);
}
/**
* 静态方法
*/
public static Integer sum(Integer a, Integer b) {
return a + b;
}
}
@FunctionalInterface
interface CalculateInterface {
/**
* 函数式接口抽象方法
*/
Integer calculate(Integer a, Integer b);
}
2.3 类名::实例方法名
函数式接口抽象方法的第一个参数是实例方法所在类的对象,剩下的参数(或无参)是实例方法的入参,且方法的返回值类型一致;
public class MethodReferencesTest {
public static void main(String[] args) {
// lambda表达式写法
boolean r1 = MethodReferencesTest.getResult((a, b) -> a.equals(b));
System.out.println("r1:" + r1);
// 方法引用(类名::实例方法名)写法
boolean r2 = MethodReferencesTest.getResult(CalculateEntity::equals);
System.out.println("r2:" + r2);
}
public static Boolean getResult(CalculateInterface calculateInterface) {
CalculateEntity a = new CalculateEntity(123);
CalculateEntity b = new CalculateEntity(456);
return calculateInterface.compare(a, b);
}
}
class CalculateEntity {
private Integer num;
public CalculateEntity(Integer num) {
this.num = num;
}
/**
* 实例方法
*/
public Boolean equals(CalculateEntity entity) {
return this.num.equals(entity.num);
}
}
@FunctionalInterface
interface CalculateInterface {
/**
* 函数式接口抽象方法
*/
Boolean compare(CalculateEntity a, CalculateEntity b);
}
// 运行结果
r1:false
r2:false
2.4 类名::new
函数式接口抽象方法的形参列表与类的构造方法的一致,且抽象方法返回的类型是该类名的类型;
public class MethodReferencesTest {
public static void main(String[] args) {
// lambda表达式写法
CalculateEntity r1 = MethodReferencesTest.getResult(num -> new CalculateEntity(num));
System.out.println("r1:" + r1);
// 方法引用(类名::new)写法
CalculateEntity r2 = MethodReferencesTest.getResult(CalculateEntity::new);
System.out.println("r2:" + r2);
}
public static CalculateEntity getResult(CalculateInterface calculateInterface) {
return calculateInterface.generateEntity(123);
}
}
class CalculateEntity {
private Integer num;
/**
* 构造方法
*/
public CalculateEntity(Integer num) {
this.num = num;
}
@Override
public String toString() {
return "num = " + num;
}
}
@FunctionalInterface
interface CalculateInterface {
/**
* 函数式接口抽象方法
*/
CalculateEntity generateEntity(Integer num);
}
// 运行结果
r1:num = 123
r2:num = 123
2.5 类名[]::new
函数式接口抽象方法的参数是int类型或者Integer类型,表示数组长度,抽象方法的返回值类型是该类名类型的数组;
public class MethodReferencesTest {
public static void main(String[] args) {
// lambda表达式写法
CalculateEntity[] r1 = MethodReferencesTest.getResult(length -> new CalculateEntity[length]);
System.out.println("r1:" + Arrays.toString(r1));
// 方法引用(类名[]::new)写法
CalculateEntity[] r2 = MethodReferencesTest.getResult(CalculateEntity[]::new);
System.out.println("r2:" + Arrays.toString(r2));
}
public static CalculateEntity[] getResult(CalculateInterface calculateInterface) {
return calculateInterface.generateEntityArr(5);
}
}
class CalculateEntity {
private int num;
@Override
public String toString() {
return "num = " + num;
}
}
@FunctionalInterface
interface CalculateInterface {
/**
* 函数式接口抽象方法
*/
CalculateEntity[] generateEntityArr(Integer length);
}
// 运行结果
r1:[null, null, null, null, null]
r2:[null, null, null, null, null]
来源:https://blog.csdn.net/gu19930914/article/details/115705383
标签:MethodReferencesTest,特性,Java8,num,引用,Integer,CalculateEntity,public,r1 From: https://www.cnblogs.com/hefeng2014/p/17760200.html