java8中的方法引用與構(gòu)造器引用

java8中的方法引用與構(gòu)造器引用

方法引用：若Lambda體中的內(nèi)容有方法已經(jīng)實(shí)現(xiàn)了，我們可以使用“方法引用”

主要的三種語法格式：

1. 對象::實(shí)例名
2. 類::靜態(tài)方法名
3. 類::實(shí)例方法名

注意：

1. Lmabda體中調(diào)用方法的參數(shù)列表與返回值類型要與函數(shù)式接口中抽象方法的函數(shù)列表和返回值類型保持一致

2. 若Lambda參數(shù)列表中的第一參數(shù)是 實(shí)例方法的調(diào)用者，而第二個(gè)參數(shù)是 實(shí)例方法的參數(shù)時(shí)，可以使用ClassName::method

   public class Employee {
   
   private String name;
   private int age;
   private double salary;
   
   public Employee() {
       super();
   }
   
   public  Employee(int age){
       this.age = age;
   }
   
   public Employee(String name, int age, double salary) {
       super();
       this.name = name;
       this.age = age;
       this.salary = salary;
   }
   
   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 double getSalary() {
       return salary;
   }
   
   public void setSalary(double salary) {
       this.salary = salary;
   }
   
   @Override
   public String toString() {
       return "Employee{" +
               "name='" + name + '\'' +
               ", age=" + age +
               ", salary=" + salary +
               '}';
   }
   }

   //對象::實(shí)例方法名
   @Test
   public void test1(){
       PrintStream ps1 = System.out;
       Consumer<String> con = (x) -> ps1.println(x);
   
       PrintStream ps = System.out;
       Consumer<String> con1 = ps::println;
   
       Consumer<String> con2 = System.out::println;
       con2.accept("abcdef");
   }
   
   @Test
   public void test2(){
       Employee employee = new Employee();
       Supplier<String> sup = () -> employee.getName();
       String str = sup.get();
       System.out.println(str);
   
       Supplier<String> sup2 = employee::getName;
       String str2 = sup2.get();
       System.out.println(str2);
   
   }

   //類：靜態(tài)方法名
   @Test
   public void test3(){
       Comparator<Integer> com = (x, y) -> Integer.compare(x, y);
   
       Comparator<Integer> com1 = Integer::compare;
   }

   構(gòu)造器引用

   格式：ClassName::new
   注意：需要調(diào)用的構(gòu)造器的參數(shù)列表要與函數(shù)式接口中抽象方法的參數(shù)列表保持一致

   public class Employee {
   
   private String name;
   private int age;
   private double salary;
   
   public Employee() {
       super();
   }
   
   public  Employee(int age){
       this.age = age;
   }
   
   public Employee(String name, int age, double salary) {
       super();
       this.name = name;
       this.age = age;
       this.salary = salary;
   }
   
   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 double getSalary() {
       return salary;
   }
   
   public void setSalary(double salary) {
       this.salary = salary;
   }
   
   @Override
   public String toString() {
       return "Employee{" +
               "name='" + name + '\'' +
               ", age=" + age +
               ", salary=" + salary +
               '}';
   }
   }

   //構(gòu)造器引用
   @Test
   public void test5(){
       Supplier<Employee> sup = () -> new Employee();
   
       //構(gòu)造器引用方式
       Supplier<Employee> sup2 = Employee::new;
       Employee employee = sup2.get();
       System.out.println(employee);
   }
   
   @Test
   public void test6(){
       Function<Integer, Employee> fun = (x) -> new Employee(x);
   
       Function<Integer, Employee> fun2 = Employee::new;
       Employee emp = fun2.apply(101);
       System.out.println(emp);
   
   }

   數(shù)組引用

   格式：Type[ ]::new;

   //數(shù)組引用
   @Test
   public void test7(){
       Function<Integer, String[]> fun = (x) -> new String[x];
       String[] strs = fun.apply(10);
       System.out.println(strs.length);
   
       Function<Integer, String[]> fun2 = String[]::new;
       String[] strs2 = fun2.apply(20);
       System.out.println(strs2.length);
   }