javaJSE---Lambda表达式

本章概述：本章主要讲了Lambda表达式在Java中的使用，Lambda表达式的介绍，Lambda表达式的使用，函数式接口，Lambda表达式的原理。

本章概述：

一、funtionref

1)Demo1

2)Demo2

3)Demo3

4)Demo4

二、lambda

1)LambdaInterface

2)LambdaTest

3)Student

4)StudentDao

5)Teacher

6)TeacherDao

三、why1

1)Student

2)Test

四、why2

1)AgrFilter

2)ScoreFilter

3)StudentFilter

4)Test

五、why3

1）Test

六、why4

1）Test

七、LambdaDemo

八、LambdaInterface

-----------------------------------------------------------------------------------------------------------------------------

一、funtionref

1)Demo1.java

public class Demo1 {
static String put(){
System.out.println("put... ...");
return "put";
}
public static void getNum(int num){
System.out.println("num:"+num);
}
public static String toUpperCase(String str){
return str.toUpperCase();
}
public static Integer getStrLength(String str1,String str2){
return str1.length()+str2.length();
}
public static void main(String[] args) {
System.out.println(put());
Supplier<String> s1 =()->Demo1.put();
Supplier<String> s2 =()->{return Demo1.put();};
Supplier<String> s3 =Demo1::put;
System.out.println(s1.get());
System.out.println(s2.get());
System.out.println(s3.get());
Consumer<Integer> consumer1 = (num)->Demo1.getNum(num);
Consumer<Integer> consumer2 = Demo1::getNum;
consumer1.accept(200);
consumer2.accept(300);
Function<String,String> f1 = (str)->str.toUpperCase();
Function<String,String> f2 = (str)->{return Demo1.toUpperCase(str);};
Function<String,String> f3 = (str)->Demo1.toUpperCase(str);
Function<String,String> f4 = Demo1::toUpperCase;
Function<String,String> f5 = Fun::toUpperCase;
System.out.println(f1.apply("abcdefg"));
System.out.println(f2.apply("hijklmn"));
System.out.println(f3.apply("opqrst"));
System.out.println(f4.apply("uvw"));
System.out.println(f5.apply("xyz"));
BiFunction<String,String,Integer> b1 = Demo1::getStrLength;
BiFunction<String,String,Integer> b2 = (a,b)->Demo1.getStrLength(a,b);
BiFunction<String,String,Integer> b3 = (a,b)->{return Demo1.getStrLength(a,b);};
System.out.println(b1.apply("45679","asffg"));
System.out.println(b2.apply("45679","asffg"));
System.out.println(b3.apply("45679","asffg"));
}
}
class Fun{
public static String toUpperCase(String str){
return str.toUpperCase();
}
}

2）Demo2.java

public class Demo2 {
public void getNum(int num){
System.out.println("num:"+num);
}
public String toUpperCase(String str){
return str.toUpperCase();
}
public Integer getStrLength(String str1,String str2){
return str1.length()+str2.length();
}
public static void main(String[] args) {
new Demo2().getNum(10);
Consumer<Integer> c1 =(num)->new Demo2().getNum(num);
Consumer<Integer> c2 =(num)->{new Demo2().getNum(num);};
Consumer<Integer> c3 = new Demo2()::getNum;
c1.accept(123);
c2.accept(123);
c3.accept(123);
Function<String,String> f1 = (str)->str.toUpperCase();
Function<String,String> f2 = (str)->new Demo2().toUpperCase(str);
Function<String,String> f3 = (str)->{return new Demo2().toUpperCase(str);};
Function<String,String> f4 = new Demo2()::toUpperCase;
System.out.println(f1.apply("sdfg"));
System.out.println(f2.apply("sdfg"));
System.out.println(f3.apply("sdfg"));
System.out.println(f4.apply("sdfg"));
BiFunction<String,String,Integer> bf1 = (str1,str2)->new Demo2().getStrLength(str1,str2);
BiFunction<String,String,Integer> bf2 = (str1,str2)->{return new Demo2().getStrLength(str1,str2);};
BiFunction<String,String,Integer> bf3 = new Demo2()::getStrLength;
System.out.println(bf1.apply("454665", "sddvv"));
System.out.println(bf2.apply("454665", "sddvv"));
System.out.println(bf3.apply("454665", "sddvv"));
}
}

3)Demo3.java

public class Demo3 {
public static void main(String[] args) {
Consumer<Too> c1 =(too)->new Too().foo();
//
Consumer<Too> c2 =(too)->new Too2().foo();
不常用
Consumer<Too> c3 = Too::foo;
c1.accept(new Too());
//
c2.accept(new Too());
c3.accept(new Too());
BiConsumer<Too2,Integer> bc1 = (too2,i)->new Too2().show(i);
BiConsumer<Too2,Integer> bc2 =Too2::show;
bc1.accept(new Too2(),233);
bc2.accept(new Too2(),566);
BiFunction<Exec,String,Integer> bf1 = (e,s)->new Exec().getNum(s);
BiFunction<Exec,String,Integer> bf2 = Exec::getNum;
System.out.println(bf1.apply(new Exec(), "123"));
System.out.println(bf2.apply(new Exec(), "789"));
}
}
class Exec{
public int getNum(String str){
return 1;
}
}
class Too{
public Integer get(String str){
return 1;
}
public void foo(){
System.out.println("foo----Too");
}
}
class Too2{
public Integer get(String str){
return 1;
}
public void foo(){
System.out.println("foo2----Too2");
}
public void show(int i){
System.out.println("show:" + i);
}
}

4)Demo4.java

public class Demo4 {
public static void main(String[] args) {
Supplier<Person> s1 = ()->new Person();
s1.get();
Supplier<Person> s2 = Person::new;
s2.get();
Supplier<ArrayList> s3 = ArrayList::new;
Supplier<Set> s4 = HashSet::new;
Supplier<Thread> s5 = Thread::new;
Supplier<String> s6 = String::new;
//
Supplier<Integer> s7 = Integer::new;
Supplier<Account> s8 = Account::new;
s8.get();
Function<Integer,Account> f1 = (i)->new Account(i);
Function<Integer,Account> f2 = Account::new;
f1.apply(24);
f2.apply(22);
Consumer<String> c1 =(name)->new Account(name);
Consumer<String> c2 =Account::new;
c1.accept("张一通");
c2.accept("黄小凡");
}
}
class Account{
public Account(){
System.out.println("Account的空构造方法被调用了... ...");
}
public Account(int age){
System.out.println("Account的一个参数age的构造方法被调用了... ..."+age);
}
public Account(String name){
System.out.println("Account的一个参数name的构造方法被调用了... ..."+name);
}
}
class Person{
public Person(){
System.out.println("Person的空构造方法被调用了... ...");
}
}

二、lambda

1)LambdaInterface.java

@FunctionalInterface
public interface LambdaInterface {
int get(int num);
}

2)LambdaTest.java

public class LambdaTest {
public static void main(String[] args) throws Exception {
//
Runnable runnable = new Runnable() {
//
@Override
//
public void run() {
//
System.out.println("running--1!");
//
}
//
};
//
runnable.run();
//
Runnable runnable1 = ()-> System.out.println("running--2!");
//
Runnable runnable2 = ()-> {
//
System.out.println("running--3!");
//
};
//
runnable1.run();
//
runnable2.run();
//
//
Callable<String> callable = new Callable<String>() {
//
public String call() throws Exception {
//
return "huang";
//
}
//
};
//
System.out.println(callable.call());
//
//
Callable<String> callable1 = ()->{return "huang2";};
//
Callable<String> callable2 = ()->"huang3";
//
System.out.println(callable1.call());
//
System.out.println(callable2.call());
//
//
StudentDao dao = new StudentDao() {
//
@Override
//
public void insert(Student student) {
//
System.out.println("插入第一个学生记录"+student);
//
}
//
};
//
dao.insert(new Student());
//
StudentDao dao1 = (student) -> System.out.println("插入第二个学生记录"+student);
//
StudentDao dao2 = (Student student)-> System.out.println("插入第三个学生记录"+student);
//
StudentDao dao3 = (student )->{
//
System.out.println("插入第四个学生记录"+student);
//
};
//
StudentDao dao4 = (Student student)->{
//
System.out.println("插入第五个学生记录"+student);
//
};
//
StudentDao dao5 = student -> System.out.println("插入第六个学生记录"+student);
//
StudentDao dao6 = student -> {
//
System.out.println("插入第七个学生记录"+student);
//
};
//
//
dao1.insert(new Student());
//
dao2.insert(new Student());
//
dao3.insert(new Student());
//
dao4.insert(new Student());
//
dao5.insert(new Student());
//
dao6.insert(new Student());
//
//
TeacherDao teacherDao = new TeacherDao() {
//
@Override
//
public int get(Teacher teacher) {
//
return 1;
//
}
//
};
//
System.out.println(teacherDao.get(new Teacher()));
//
TeacherDao teacherDao1 = (teacher)-> {return 2;};
//
TeacherDao teacherDao2 = (teacher)->3;
//
TeacherDao teacherDao3 = teacher -> {return 4;};
//
TeacherDao teacherDao4 = teacher->5;
//
System.out.println(teacherDao1.get(new Teacher()));
//
System.out.println(teacherDao2.get(new Teacher()));
//
System.out.println(teacherDao3.get(new Teacher()));
//
System.out.println(teacherDao4.get(new Teacher()));
//
//
//
/*
//
*
在JDK中，提供了一些代表输入和输出的接口，他们本身是没有什么意义的，
//
*
只是为了方便的使用lambda表达式来编写代码，从而获取对应的执行结果。
//
*
//
*/
Supplier<Integer> supplier =new Supplier<Integer>() {
@Override
public Integer get() {
return 1;
}
};
//
Supplier<Integer> supplier = ()->1;
//
System.out.println(supplier.get());
//
//
Consumer<String> consumer = new Consumer<String>() {
@Override
public void accept(String s) {
System.out.println(s);
}
};
//
Consumer<String> consumer = (s)-> System.out.println(s);
//
consumer.accept("huang");
//
Function<Integer,String> function = new Function<Integer, String>() {
@Override
public String apply(Integer integer) {
return integer + "huang2";
}
};
//
Function<Integer,String> function = (i)->i+"huang3";
//
Function<Integer,String> function1 = (Integer i)->{return i+"huang4";};
//
System.out.println(function.apply(2003));
//
System.out.println(function1.apply(2002));
BiFunction<String,String,Integer> bf = (a,b)->a.length()+b.length();
System.out.println(bf.apply("张一通","很帅"));
Runnable runnable1 = ()-> System.out.println(get());
Runnable runnable2 = ()->{
String str = find();
System.out.println(str);
};
Runnable runnable3 = ()->exec();
//
Runnable runnable4 = ()->1;
//
Runnable runnable5 = ()->"OK";
Runnable runnable6 = ()->get();
//
Runnable runnable7 =()-> true?1:2;
runnable1.run();
runnable2.run();
runnable3.run();
LambdaInterface li1 = new LambdaInterface() {
@Override
public int get(int num) {
return num;
}
};
System.out.println(li1.get(200));
//
LambdaInterface li2 = (num) ->get(num);
//
LambdaInterface li3 = (num)-> System.out.println(num);
//
LambdaInterface li4 = (num) -> {return get(num);};
LambdaInterface li5 = (num)->{return num;};
LambdaInterface li6 = (num)->num;
LambdaInterface li7 = num->{return num;};
LambdaInterface li8 = num -> num;
System.out.println(li5.get(300));
Function<Integer,Integer> function = (num)->num;
System.out.println(function.apply(100));
Consumer<Integer> consumer1 = (num)-> System.out.println(num);
consumer1.accept(1000);
Consumer<Integer> consumer2 = (num)->getNum(num);
consumer2.accept(2000);
Function<String,String> f1 = (str)->str.toUpperCase();
Function<String,String> f2 = (str)->toUpperCase(str);
System.out.println(f1.apply("abcdefg"));
System.out.println(f2.apply("cdsefgggg"));
BiFunction<String,String,Integer> biFunction1 = (a,b)->a.length()+b.length();
System.out.println(biFunction1.apply("张一通", "真帅"));
BiFunction<String,String,Integer> biFunction2 = (a,b)->getStrLength(a,b);
System.out.println(biFunction2.apply("张一通", "非常帅"));
}
public static void getNum(int num){
System.out.println(num);
}
public static String toUpperCase(String str){
return str.toUpperCase();
}
public static Integer getStrLength(String str1,String str2){
return str1.length()+str2.length();
}
public static int get(){
return 1;
}
public static String find(){
return "find";
}
public static void exec(){
find();
}
}

3)Student.java

public class Student {
}

4)StudentDao.java

public interface StudentDao {
public void insert(Student student);
}

5)Teacher.java

public class Teacher{
}

 6)TeacherDao.java

public interface TeacherDao {
public int get(Teacher teacher);
}

三、why1

1)Student.java

public class Student {
private String name;
private int age;
private int score;
public Student() {
}
public Student(String name, int age, int score) {
this.name = name;
this.age = age;
this.score = 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;
}
@Override
public String toString() {
return "Student{" +
"name='" + name + ''' +
", age=" + age +
", score=" + score +
'}';
}
}

2)Test.java

public class Test {
public static void main(String[] args) {
ArrayList<Student> list = new ArrayList<>();
list.add(new Student("zhangfei",18,75));
list.add(new Student("guanyu",20,70));
list.add(new Student("zhaoyun",26,75));
list.add(new Student("liubei",30,85));
list.add(new Student("huangzhong",23,90));
//查询年龄大于25岁学生的信息
getByAge(list);
System.out.println("******************************************");
//查询成绩大于80学生的信息
getByScore(list);
}
public static void getByAge(ArrayList<Student> students){
ArrayList<Student> list = new ArrayList<>();
for(Student student : students){
if(student.getAge()>25){
list.add(student);
}
}
for(Student student : list){
System.out.println(student);
}
}
public static void getByScore(ArrayList<Student> students){
ArrayList<Student> list = new ArrayList<>();
for(Student student : students){
if(student.getScore()>80){
list.add(student);
}
}
for(Student student : list){
System.out.println(student);
}
}
}

四、why2

1）AgeFilter.java

public class AgeFilter implements StudentFilter{
@Override
public boolean compare(Student student) {
return student.getAge() > 25;
}
}

2)ScoreFilter.java

public class ScoreFilter implements StudentFilter{
@Override
public boolean compare(Student student) {
return student.getScore() > 80;
}
}

3)StudentFilter.java

public interface StudentFilter {
public boolean compare(Student student);
}

4)Test.java

public class Test {
public static void main(String[] args) {
ArrayList<Student> list = new ArrayList<>();
list.add(new Student("zhangfei",18,69));
list.add(new Student("guanyu",20,70));
list.add(new Student("zhaoyun",26,75));
list.add(new Student("liubei",30,85));
list.add(new Student("huangzhong",23,90));
//查询年龄大于25岁的学生信息
getByFilter(list,new AgeFilter());
//查询分数大于80分的学生信息
System.out.println("**************************************************");
getByFilter(list,new ScoreFilter());
}
public static void getByFilter(ArrayList<Student> students,StudentFilter filter){
ArrayList<Student> list = new ArrayList<>();
for(Student student : students){
if(filter.compare(student)){
list.add(student);
}
}
for(Student student :list){
System.out.println(student);
}
}
}

五、why3

1）Test.java

public class Test {
public static void main(String[] args) {
ArrayList<Student> list = new ArrayList<>();
list.add(new Student("zhangfei",18,69));
list.add(new Student("guanyu",20,70));
list.add(new Student("zhaoyun",26,75));
list.add(new Student("liubei",30,85));
list.add(new Student("huangzhong",23,90));
//查询年龄大于25岁的学生信息
getByFilter(list, new StudentFilter() {
@Override
public boolean compare(Student student) {
return student.getAge()>25;
}
});
//查询成绩大于80分的学生信息
System.out.println("************************************");
getByFilter(list, new StudentFilter() {
@Override
public boolean compare(Student student) {
return student.getScore()>80;
}
});
//查询名字长度大于6的学生信息
getByFilter(list, new StudentFilter() {
@Override
public boolean compare(Student student) {
return student.getName().length() > 6;
}
});
}
public static void getByFilter(ArrayList<Student> students, StudentFilter filter){
ArrayList<Student> list = new ArrayList<>();
for(Student student : students){
if(filter.compare(student)){
list.add(student);
}
}
for(Student student : list){
System.out.println(student);
}
}
}

六、why4

1)Test.java

public class Test {
public static void main(String[] args) {
ArrayList<Student> list = new ArrayList<>();
list.add(new Student("zhangfei",18,69));
list.add(new Student("guanyu",20,70));
list.add(new Student("zhaoyun",26,75));
list.add(new Student("liubei",30,85));
list.add(new Student("huangzhong",23,90));
//查询年龄大于25岁的学生信息
getByFilter(list,(student -> student.getAge()>25));
//查询成绩大于80分的学生信息
System.out.println("***************************************");
getByFilter(list,(student -> student.getScore()>80));
//查询姓名长度大于6的学生成绩
System.out.println("***************************************");
getByFilter(list,(student) ->student.getName().length()>6 );
}
public static void getByFilter(ArrayList<Student> students, StudentFilter filter){
ArrayList<Student> list = new ArrayList<>();
for(Student student : students){
if(filter.compare(student)){
list.add(student);
}
}
for(Student student :list){
System.out.println(student);
}
}
}

七、LambdaDemo.java

public class LambdaDemo {
public static void main(String[] args) {
Thread thread = new Thread(new Runnable() {
@Override
public void run() {
System.out.println("Running!");
}
});
thread.start();
new Thread(()-> System.out.println("Running!")).start();
List<String> list = Arrays.asList("java","go","python","scala","javascript");
Collections.sort(list, new Comparator<String>() {
@Override
public int compare(String o1, String o2) {
return o1.length()-o2.length();
}
});
for(String str : list){
System.out.println(str);
}
Collections.sort(list,(a,b)->a.length()-b.length());
list.forEach(System.out::println);
}
}

八、LambdaInterface.java

@FunctionalInterface
public interface LambdaInterface {
public void add(int a,int b);
//
public void sub(int a,int b);
}

最后

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