函数式接口： java类型中的接口，只包含一个方法的接口
@FunctionalInterface
注解标注在类上
一但超过一个接口就代表不是函数式接口，就会报错
个人理解就是匿名函数是多态实现写在具体使用中
第一种
未使用前
Thread thread = new Thread(new Runnable() {
@Override
public void run() {
System.out.println("running......");
}
});
thread.start();
使用后
new Thread(()->{
System.out.println("running......");
}).start();
第二种
未使用前
List<String> list = Arrays.asList("java", "javascript", "scala", "python");
Collections.sort(list, new Comparator<String>() {
@Override
public int compare(String s, String t1) {
return s.length()-t1.length();
}
});
for (String str:list){
System.out.println(str);
}
使用后
List<String> list = Arrays.asList("java", "javascript", "scala", "python");
Collections.sort(list,(a,b)->a.length()-b.length());
list.forEach(System.out::println);
第三种优化策略模式
使用前策略模式表达式优化前
package why1;
import java.util.Comparator;
public interface StudentFilter {
boolean compare(Student student);
}
package why1;
import why1.StudentFilter;
public class AgeFilter implements StudentFilter {
@Override
public boolean compare(Student student) {
return student.getAge()>14;
}
}
package why1;
import why1.StudentFilter;
public class ScoreFilter implements StudentFilter {
@Override
public boolean compare(Student student) {
return student.getScore()>50;
}
}
package why1;
public class Student {
private String name;
private int age;
private int score;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public int getScore() {
return score;
}
public void setScore(int score) {
this.score = score;
}
public Student(String name, int age, int score) {
this.name = name;
this.age = age;
this.score = score;
}
@Override
public String toString() {
return "Student{" +
"name='" + name + '\'' +
", age=" + age +
", score=" + score +
'}';
}
}
package lambda;
import why1.AgeFilter;
import why1.ScoreFilter;
import why1.Student;
import why1.StudentFilter;
import java.util.*;
public class LambdaDemo {
public static void main(String[] args) {
ArrayList<Student> students = new ArrayList<>();
students.add(new Student("zhangsan1",12,234));
students.add(new Student("zhangsan2",34,32));
students.add(new Student("zhangsan3",54,111113));
students.add(new Student("zhangsan4",14,32434));
students.add(new Student("zhangsan5",64,32535));
students.add(new Student("zhangsan6",88,43));
students.add(new Student("zhangsan7",34,32));
getByFilter(students, new AgeFilter());
System.out.println("--------------------------------------");
getByFilter(students, new ScoreFilter());
}
public static void getByFilter(ArrayList<Student> students, StudentFilter studentFilter){
ArrayList<Student> list = new ArrayList<>();
for (Student student:students){
if(studentFilter.compare(student)){
list.add(student);
}
}
printStudent(list);
}
public static void printStudent(ArrayList<Student> students){
for(Student student:students){
System.out.println(student);
}
}
}
优化后
package why1;
public class Student {
private String name;
private int age;
private int score;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public int getScore() {
return score;
}
public void setScore(int score) {
this.score = score;
}
public Student(String name, int age, int score) {
this.name = name;
this.age = age;
this.score = score;
}
@Override
public String toString() {
return "Student{" +
"name='" + name + '\'' +
", age=" + age +
", score=" + score +
'}';
}
}
package why1;
import java.util.Comparator;
@FunctionalInterface
public interface StudentFilter {
boolean compare(Student student);
}
package lambda;
import why1.Student;
import why1.StudentFilter;
import java.util.*;
public class LambdaDemo {
public static void main(String[] args) {
ArrayList<Student> students = new ArrayList<>();
students.add(new Student("zhangsan1",12,234));
students.add(new Student("zhangsan2",34,32));
students.add(new Student("zhangsan3",54,111113));
students.add(new Student("zhangsan4",14,32434));
students.add(new Student("zhangsan5",64,32535));
students.add(new Student("zhangsan6",88,43));
students.add(new Student("zhangsan7",34,32));
getByFilter(students,(o)->o.getAge()>14);
System.out.println("----------------------------------------");
getByFilter(students,(o)->o.getScore()>50);
}
public static void getByFilter(ArrayList<Student> students, StudentFilter studentFilter){
ArrayList<Student> list = new ArrayList<>();
for (Student student:students){
if(studentFilter.compare(student)){
list.add(student);
}
}
printStudent(list);
}
public static void printStudent(ArrayList<Student> students){
for(Student student:students){
System.out.println(student);
}
}
}
第四种
原始写法
public class Main {
final static String originWrite = "原始写法： ";
public static void main(String[] args) {
GreetingService2 greetingService2 = new GreetingService2();
greetingService2.sayMessage("123");
}
interface GreetingService {
void sayMessage(String message);
}
static class GreetingService2 implements GreetingService{
@Override
public void sayMessage(String message) {
System.out.println(originWrite + message);
}
}
}
当前写法
public class Main {
final static String thisWrite = "新写法： ";
public static void main(String[] args) {
GreetingService greetingService = msg-> System.out.println(thisWrite+msg);
greetingService.sayMessage("123");
}
interface GreetingService {
void sayMessage(String message);
}
}