Java8函数式编程之五：方法引用详解
方法引用详解：（method reference）
某些时候，Lambda表达式方法体的实现正好是已经存在的方法能够提供的功能，那么此时就可以用已经存在的方法替换Lambda表达式。
是Lambda的一种特殊情况，或者说是Lambda表达式的一种语法糖。
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Lambda表达式的语法与方法引用的语法对比：
1.比较1
(Trade trade) -> trade.getMoney()
Trade :: getMoney2.比较2
() -> Thread.currentThread().dumpStack()
Thread.currrntThread() :: dumpStack3.比较3
(str,i) -> str.substring(i)
String :: substring————————————————————————
实例1:
public class MethodReferenceDemo {
public static void main(String[] args){
List list = Arrays.asList("hello","world","hello world");
//使用lambda表达式
list.forEach(item -> System.out.print(item));
//使用方法引用
list.forEach(System.out :: print);
}
} ——————————————————
我们可以将方法引用分为4类：
1.类名 :: 静态方法名
2.引用名(对象名) :: 实例方法名
3.类名 :: 实例方法名
4.构造方法引用 类名 :: new
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实例1 ： 类名 :: 静态方法名
public class Student {
private String name;
private int score;
public Student(String name, int score) {
this.name = name;
this.score = score;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getScore() {
return score;
}
public void setScore(int score) {
this.score = score;
}
//写两个静态方法
//根据分数进行比较
public static int compareStudentByScore(Student student1,Student student2){
return student1.getScore() - student2.getScore();
}
//根据名字进行比较
public static int compareStudentByName(Student student1,Student student2){
return student1.getName().compareToIgnoreCase(student2.getName());
}
}
__
public class MethodReferenceTest {
public static void main(String[] args){
Student student1 = new Student("zhangsan",44);
Student student2 = new Student("lisi",55);
Student student3 = new Student("wangwu",76);
Student student4 = new Student("zhanoliu",98);
List students = Arrays.asList(student1,student2,student3,student4);
//使用lambda表达式
students.sort((s1,s2) -> Student.compareStudentByScore(s1,s2));
students.forEach(student -> System.out.println(student.getScore()));
//使用方法引用
students.sort(Student :: compareStudentByScore);
students.forEach(student -> System.out.println(student.getScore()));
}
} ————————————————
实例2 ：引用名（对象名） :: 实例方法名
public class StudentComparator {
//根据分数进行比较
public int compareStudentByScore(Student student1,Student student2){
return student1.getScore() - student2.getScore();
}
//根据名字进行比较
public int compareStudentByName(Student student1,Student student2){
return student1.getName().compareToIgnoreCase(student2.getName());
}
}——————
public class MethodReferenceTest {
public static void main(String[] args){
Student student1 = new Student("zhangsan",44);
Student student2 = new Student("lisi",55);
Student student3 = new Student("wangwu",76);
Student student4 = new Student("zhanoliu",98);
List students = Arrays.asList(student1,student2,student3,student4);
StudentComparator comparator = new StudentComparator();
//使用lambda表达式
students.sort((s1,s2) -> comparator.compareStudentByScore(s1,s2));
students.forEach(student -> System.out.println(student.getScore()));
students.sort((s1,s2) -> comparator.compareStudentByName(s1,s2));
students.forEach(student -> System.out.println(student.getName()));
//使用方法引用
students.sort(comparator :: compareStudentByScore);
students.forEach(student -> System.out.println(student.getScore()));
students.sort(comparator :: compareStudentByName);
students.forEach(student -> System.out.println(student.getName()));
}
}
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实例3 ： 类名 :: 实例方法名
public class Student {
private String name;
private int score;
public Student(String name, int score) {
this.name = name;
this.score = score;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getScore() {
return score;
}
public void setScore(int score) {
this.score = score;
}
//比上文更好的设计，使用当前的score与传进来的score进行比较
public int compareByScore(Student student){
return this.getScore() - student.getScore();
}
public int compareByName(Student student){
return this.getName().compareToIgnoreCase(student.getName());
}
}
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public class MethodReferenceTest {
public static void main(String[] args) {
Student student1 = new Student("zhangsan", 44);
Student student2 = new Student("lisi", 55);
Student student3 = new Student("wangwu", 76);
Student student4 = new Student("zhanoliu", 98);
List students = Arrays.asList(student1, student2, student3, student4);
students.sort(Student::compareByScore);
students.forEach(student -> System.out.println(student.getScore()));
}
} ————————————————————————
实例4 ： 类名 :: new
public class MethodReferenceTest {
public String getString(Supplier supplier){
return supplier.get() +"test";
}
public String getString2(String str , Function function){
return function.apply(str);
}
public static void main(String[] args) {
Student student1 = new Student("zhangsan", 44);
Student student2 = new Student("lisi", 55);
Student student3 = new Student("wangwu", 76);
Student student4 = new Student("zhanoliu", 98);
List students = Arrays.asList(student1, student2, student3, student4);
MethodReferenceTest test = new MethodReferenceTest();
System.out.println(test.getString(String :: new));
System.out.println(test.getString2("hello",String ::new));
}
}
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好的，方法引用的全部类型就是上面这么多了，总结来说，方法引用就是lambda表达式的一种语法糖而已。
下一篇博客开始，我们开始学习Java8中最重要的一个部分，也就是Stream（流）。