java8新特性之--函数式接口加方法引用与构造器引用详细讲解

public class TestLambda3 {
  //Predicate<T> 断言型接口：
  @Test
  public void test4(){
    List<String> list = Arrays.asList("Hello", "atguigu", "Lambda", "www", "ok");
    List<String> strList = filterStr(list, (s) -> s.length() > 3);
    for (String str : strList) {
      System.out.println(str);
    }
  }
  //需求：将满足条件的字符串，放入集合中
  public List<String> filterStr(List<String> list, Predicate<String> pre){
    List<String> strList = new ArrayList<>();
    for (String str : list) {
      if(pre.test(str)){
        strList.add(str);
      }
    }
    return strList;
  }
}

public class TestLambda3 {
  //Function<T, R> 函数型接口：
  @Test
  public void test3(){
    String newStr = strHandler("\t\t\t 感谢大家观看", (str) -> str.trim());
    System.out.println(newStr);
    String subStr = strHandler("谢谢", (str) -> str.substring(2, 5));
    System.out.println(subStr);
  }
  //需求：用于处理字符串
  public String strHandler(String str, Function<String, String> fun){
    return fun.apply(str);
  }
}

public class TestLambda3 {  
  //Supplier<T> 供给型接口 :
  @Test
  public void test2(){
    List<Integer> numList = getNumList(10, () -> (int)(Math.random() * 100));
    for (Integer num : numList) {
      System.out.println(num);
    }
  }
  //需求：产生指定个数的整数，并放入集合中
  public List<Integer> getNumList(int num, Supplier<Integer> sup){
    List<Integer> list = new ArrayList<>();
    for (int i = 0; i < num; i++) {
      Integer n = sup.get();
      list.add(n);
    }
    return list;
  }

  //Consumer<T> 消费型接口 :
  @Test
  public void test1(){
    happy(10000, (m) -> System.out.println("大家好一瓶水：" + m + "元"));
  } 
  public void happy(double money, Consumer<Double> con){
    con.accept(money);
  }
}

//对象的引用 :: 实例方法名
  @Test
  public void test2(){
    Employee emp = new Employee(101, "张三", 18, 9999.99);
    Supplier<String> sup = () -> emp.getName();
    System.out.println(sup.get());
    System.out.println("----------------------------------");
    Supplier<String> sup2 = emp::getName;
    System.out.println(sup2.get());
  }

//类名 :: 实例方法名
  @Test
  public void test5(){
    BiPredicate<String, String> bp = (x, y) -> x.equals(y);
    System.out.println(bp.test("abcde", "abcde"));
    System.out.println("-----------------------------------------");
    BiPredicate<String, String> bp2 = String::equals;
    System.out.println(bp2.test("abc", "abc"));
    System.out.println("-----------------------------------------");
    Function<Employee, String> fun = (e) -> e.show();
    System.out.println(fun.apply(new Employee()));
    System.out.println("-----------------------------------------");
    Function<Employee, String> fun2 = Employee::show;
    System.out.println(fun2.apply(new Employee()));
  }

  //类名 :: 静态方法名
  @Test
  public void test4(){
    Comparator<Integer> com = (x, y) -> Integer.compare(x, y);
    System.out.println("-------------------------------------");
    Comparator<Integer> com2 = Integer::compare;
  }
  @Test
  public void test3(){
    BiFunction<Double, Double, Double> fun = (x, y) -> Math.max(x, y);
    System.out.println(fun.apply(1.5, 22.2));
    System.out.println("--------------------------------------------------");
    BiFunction<Double, Double, Double> fun2 = Math::max;
    System.out.println(fun2.apply(1.2, 1.5));
  }

  @Test
  public void test7(){
    Function<String, Employee> fun = Employee::new;
    BiFunction<String, Integer, Employee> fun2 = Employee::new;
  }

//数组引用
  @Test
  public void test8(){
    Function<Integer, String[]> fun = (args) -> new String[args];
    String[] strs = fun.apply(10);
    System.out.println(strs.length);
    System.out.println("--------------------------");
    Function<Integer, Employee[]> fun2 = Employee[] :: new;
    Employee[] emps = fun2.apply(20);
    System.out.println(emps.length);
  }