Java中Lambda表达式用法介绍

@Test
public void test(){
    // () -> System.out.println("Hello");
    Runnable a = new Runnable(){
     @Override
     public void run(){
        System.out.println("Hello")
    }
    };
    //等同于
    Runnable a1 = () -> System.out.println("Hello");
    a1.run();
}

@Test
public void test(){
    //Consumer被注解@FunctionalInterface的接口（函数式接口） 唯一抽象方法 void accept(T t);
    //左侧参数 -> 右侧执行体
    Consumer<String> con = (x) -> System.out.println(x);
                         // x -> System.out.println(x);
    con.accept("hahah");
}

@Test
public void test(){
    //Comparator被注解@FunctionalInterface的接口 举例抽象方法 int compare(T o1,T o2);
    Comparator<Integer> com = (x,y) -> {
      System.out.println("hhaha0");
      return (x < y) ? -1 : ((x == y) ? 0 : 1);
    };
    com.compare(1,2);
}

class Employee {
    private String name;
    private int age;
    private double salary;
​
    //省略 get and set and constructor
​
}
interface MyPredicate<T> {
    boolean test(T t);
}
public class Test{
    static List<Employee> list = Arrays.asList(
            new Employee("张三",10,1),
            new Employee("里斯",20,1),
            new Employee("王五",16,1),
            new Employee("二三",30,1)
    );
    public static List<Employee> filterEmployee(List<Employee> list,MyPredicate<Employee> mp){
        List<Employee> emps = new ArrayList<>();
        for (Employee employee : list) {
            if(mp.test(employee)){
                emps.add(employee);
            }
        }
        return emps;
 }
    @org.junit.Test
    public void test1(){
        //需要使用自定义的方法
        List<Employee> list2 = filterEmployee(list,(e) -> e.getAge() >= 15);
        list2.stream().map(Employee::getName).forEach(System.out::println);
    }
    @org.junit.Test
    public void test2(){
        //可以使用stream进行list集合的过滤  不使用自定义接口
        List<Employee> list2 = list.stream().filter((e) -> e.getAge() >= 15).collect(Collectors.toList());
        list2.stream().map(Employee::getName).forEach(System.out::println);
    }
}

@FunctionalInterface
interface MyFun{
    Integer getValue(Integer num);
}
public class Test{
    @org.junit.Test
    public void Test(){
        operation(100,num -> ++num);
    }
    
    public Integer operation(Integer num,MyFun mf){
        return mf.getValue(num);
    }
}

class Employee {
    private String name;
    private int age;
    private double salary;
​
    @Override
    public String toString() {
        return "["+this.name+","+this.getAge()+","+this.getSalary()+"]";
    }
    //省略 getter and setter  and constructor
}
​
public class Test {
    List<Employee> list = Arrays.asList(
            new com.bilibili.lambda.test1.Employee("张三",10,1),
            new com.bilibili.lambda.test1.Employee("里斯",20,1),
            new com.bilibili.lambda.test1.Employee("王五",16,1),
            new Employee("二三",30,1)
    );
    @org.junit.Test
    public void test(){
        Collections.sort(list,(e1,e2) -> {
            if(e1.getAge() == e2.getAge()){
                return e1.getName().compareTo(e2.getName());
            }else{
                //比较年龄大小
                return Integer.compare(e1.getAge(),e2.getAge());
            }
        });
        for (Employee e: list) {
            System.out.println(e);
        }
    }
}

 
class Test{
    @org.junit.Test
    publilc void test(){
        happy(10000,(money)->System.out.println("happy消费"+money+"元"));
    }
    public void happy(double money,Consumer<double> con){
        con.accept(money);
    }
}

class Test{
    //对象::实例方法名
    @org.junit.Test
    public void test(){
        Consumer<String> con = (x) -> System.out.println(x);
        con.accept("haha");
        Consumer<String> con2 = System.out::println;
        con2.accept("haha");
    }
    //类::静态方法名
    @org.junit.Test
    public void test2(){
        Comparator<Integer> com = (x,y) -> Integer.compare(x,y);
        Comparator<Integer> com2 = Integer::compare;
        com.compare(1,2);
        com2.compare(1,2);
    }
    //类::实例方法名
    @org.junit.Test(){
        BiPredicate<String,String> bp = (x,y) -> x.equals(y);
        bp.test("a","a");
        BiPredicate<String,String> bp2 = String::equals;
    }
}

class Test{
    @org.junit.Test
    public void test(){
        Supplier<String> sup = () -> new String();
        //这里的构造器引用取决于 接口方法的参数 的个数。 此处函数式接口 T get(); 为无参抽象方法所以String在实例化时 也是实例化无参的构造方法  其他类也适用
        Supplier<String> sup2 = String::new;
        String str = sup2.get();
    }
}