Java 版本特性

List<Employee> emps = Arrays.asList(
        new Employee(101, "张三", 18, 9999.99),
        new Employee(102, "李四", 59, 6666.66),
        new Employee(103, "王五", 28, 3333.33),
        new Employee(104, "赵六", 8, 7777.77),
        new Employee(105, "田七", 38, 5555.55)
);

//需求：获取公司中年龄小于 35 的员工信息
public List<Employee> filterEmployeeAge(List<Employee> emps){
    List<Employee> list = new ArrayList<>();
    
    for (Employee emp : emps) {
        if(emp.getAge() <= 35){
            list.add(emp);
        }
    }
    
    return list;
}

@Test
public void test3(){
    List<Employee> list = filterEmployeeAge(emps);
    
    for (Employee employee : list) {
        System.out.println(employee);
    }
}

//需求：获取公司中工资大于 5000 的员工信息
public List<Employee> filterEmployeeSalary(List<Employee> emps){
    List<Employee> list = new ArrayList<>();
    
    for (Employee emp : emps) {
        if(emp.getSalary() >= 5000){
            list.add(emp);
        }
    }
    
    return list;
}

//优化方式二：匿名内部类, 需写接口和实现类,具体看java-learning代码
@Test
public void test5(){
    List<Employee> list = filterEmployee(emps, new MyPredicate<Employee>() {
        @Override
        public boolean test(Employee t) {
            return t.getId() <= 103;
        }
    });
    
    for (Employee employee : list) {
        System.out.println(employee);
    }
}

//优化方式三：Lambda 表达式
@Test
public void test6(){
    List<Employee> list = filterEmployee(emps, (e) -> e.getAge() <= 35);
    list.forEach(System.out::println);
    
    System.out.println("------------------------------------------");
    
    List<Employee> list2 = filterEmployee(emps, (e) -> e.getSalary() >= 5000);
    list2.forEach(System.out::println);
}

//优化方式四：Stream API
@Test
public void test7(){
    emps.stream()
        .filter((e) -> e.getAge() <= 35)
        .forEach(System.out::println);
    
    System.out.println("----------------------------------------------");
    
    emps.stream()
        .map(Employee::getName)
        .limit(3)
        .sorted()
        .forEach(System.out::println);
}

public class TestLambda2 {
    
    @Test
    public void test1(){
        int num = 0;//jdk 1.7 前，必须是 final
        
        Runnable r = new Runnable() {
            @Override
            public void run() {
                System.out.println("Hello World!" + num);
            }
        };
        
        r.run();
        
        System.out.println("-------------------------------");
        
        Runnable r1 = () -> System.out.println("Hello Lambda!");
        r1.run();
    }
    
    @Test
    public void test2(){
        Consumer<String> con = x -> System.out.println(x);
        con.accept("我和我的祖国！");
    }
    
    @Test
    public void test3(){
        Comparator<Integer> com = (x, y) -> {
            System.out.println("测试多行代码");
            return Integer.compare(x, y);
        };
    }
    
    @Test
    public void test4(){
        Comparator<Integer> com = (x, y) -> Integer.compare(x, y);
    }

    //类型抢断示例
    @Test
    public void test5(){
        String[] strs = {"aaa", "bbb", "ccc"};
        
        List<String> list = new ArrayList<>();
        
        show(new HashMap<>());
    }

    public void show(Map<String, Integer> map){
        
    }
    
    //需求：对一个数进行运算
    @Test
    public void test6(){
        Integer num = operation(100, (x) -> x * x);
        System.out.println(num);
        
        System.out.println(operation(200, (y) -> y + 200));
    }
    
    public Integer operation(Integer num, Function<Integer, Integer> function){
        return function.apply(num);
    }
}

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;
    }
    
    //Function<T, R> 函数型接口：
    @Test
    public void test3(){
        String newStr = strHandler("\t\t\t 我爱我的祖国   ", (str) -> str.trim());
        System.out.println(newStr);
        
        String subStr = strHandler("我爱我的祖国", (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);
    }
    
    //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("买西瓜花了：" + m + "元"));
    } 
    
    public void happy(double money, Consumer<Double> con){
        con.accept(money);
    }
}

 //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(com.compare(1, 2));

    System.out.println("-------------------------------------");

    Comparator<Integer> com2 = Integer::compare;
    System.out.println(com.compare(2, 2));
}

@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));
}

//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());
}

@Test
public void test1() {
    PrintStream ps = System.out;
    Consumer<String> con = (str) -> ps.println(str);
    con.accept("Hello World！");

    System.out.println("--------------------------------");

    Consumer<String> con2 = ps::println;
    con2.accept("Hello Java8！");

    Consumer<String> con3 = System.out::println;
}

public class TestStreamaAPI {
    
    //1. 创建 Stream
    @Test
    public void test1(){
        //1. Collection 提供了两个方法  stream() 与 parallelStream()
        List<String> list = new ArrayList<>();
        Stream<String> stream = list.stream(); //获取一个顺序流
        Stream<String> parallelStream = list.parallelStream(); //获取一个并行流
        
        //2. 通过 Arrays 中的 stream() 获取一个数组流
        Integer[] nums = new Integer[10];
        Stream<Integer> stream1 = Arrays.stream(nums);
        
        //3. 通过 Stream 类中静态方法 of()
        Stream<Integer> stream2 = Stream.of(1,2,3,4,5,6);
        
        //4. 创建无限流
        //迭代
        Stream<Integer> stream3 = Stream.iterate(0, (x) -> x + 2).limit(10);
        stream3.forEach(System.out::println);
        
        //生成
        Stream<Double> stream4 = Stream.generate(Math::random).limit(2);
        stream4.forEach(System.out::println);
        
    }
    
    //2. 中间操作
    List<Employee> emps = Arrays.asList(
            new Employee(102, "李四", 59, 6666.66),
            new Employee(101, "张三", 18, 9999.99),
            new Employee(103, "王五", 28, 3333.33),
            new Employee(104, "赵六", 8, 7777.77),
            new Employee(104, "赵六", 8, 7777.77),
            new Employee(104, "赵六", 8, 7777.77),
            new Employee(105, "田七", 38, 5555.55)
    );
    
    /*
      筛选与切片
        filter——接收 Lambda ， 从流中排除某些元素。
        limit——截断流，使其元素不超过给定数量。
        skip(n) —— 跳过元素，返回一个扔掉了前 n 个元素的流。若流中元素不足 n 个，则返回一个空流。与 limit(n) 互补
        distinct——筛选，通过流所生成元素的 hashCode() 和 equals() 去除重复元素
     */
    
    //内部迭代：迭代操作 Stream API 内部完成
    @Test
    public void test2(){
        //所有的中间操作不会做任何的处理
        Stream<Employee> stream = emps.stream()
            .filter((e) -> {
                System.out.println("测试中间操作");
                return e.getAge() <= 35;
            });
        
        //只有当做终止操作时，所有的中间操作会一次性的全部执行，称为“惰性求值”
        stream.forEach(System.out::println);
    }
    
    //外部迭代
    @Test
    public void test3(){
        Iterator<Employee> it = emps.iterator();
        
        while(it.hasNext()){
            System.out.println(it.next());
        }
    }
    
    @Test
    public void test4(){
        emps.stream()
            .filter((e) -> {
                System.out.println("短路！"); // &&  ||
                return e.getSalary() >= 5000;
            }).limit(3)
            .forEach(System.out::println);
    }
    
    @Test
    public void test5(){
        emps.parallelStream()
            .filter((e) -> e.getSalary() >= 5000)
            .skip(2)
            .forEach(System.out::println);
    }
    
    @Test
    public void test6(){
        emps.stream()
            .distinct()
            .forEach(System.out::println);
    }
    
    /*
        映射
        map——接收 Lambda ， 将元素转换成其他形式或提取信息。接收一个函数作为参数，该函数会被应用到每个元素上，并将其映射成一个新的元素。
        flatMap——接收一个函数作为参数，将流中的每个值都换成另一个流，然后把所有流连接成一个流
     */
    @Test
    public void test1(){
        Stream<String> str = emps.stream()
            .map((e) -> e.getName());
        
        System.out.println("-------------------------------------------");
        
        List<String> strList = Arrays.asList("aaa", "bbb", "ccc", "ddd", "eee");
        
        Stream<String> stream = strList.stream()
               .map(String::toUpperCase);
        
        stream.forEach(System.out::println);
        
        Stream<Stream<Character>> stream2 = strList.stream()
               .map(TestStreamAPI1::filterCharacter);
        
        stream2.forEach((sm) -> {
            sm.forEach(System.out::println);
        });
        
        System.out.println("---------------------------------------------");
        
        Stream<Character> stream3 = strList.stream()
               .flatMap(TestStreamAPI1::filterCharacter);
        
        stream3.forEach(System.out::println);
    }

    public static Stream<Character> filterCharacter(String str){
        List<Character> list = new ArrayList<>();
        
        for (Character ch : str.toCharArray()) {
            list.add(ch);
        }
        
        return list.stream();
    }
    
    /*
        sorted()——自然排序
        sorted(Comparator com)——定制排序
     */
    @Test
    public void test2(){
        emps.stream()
            .map(Employee::getName)
            .sorted()
            .forEach(System.out::println);
        
        System.out.println("------------------------------------");
        
        emps.stream()
            .sorted((x, y) -> {
                if(x.getAge() == y.getAge()){
                    return x.getName().compareTo(y.getName());
                }else{
                    return Integer.compare(x.getAge(), y.getAge());
                }
            }).forEach(System.out::println);
    }

}

public class TestStreamAPI2 {
    
    List<Employee> emps = Arrays.asList(
            new Employee(102, "李四", 59, 6666.66, Employee.Status.BUSY),
            new Employee(101, "张三", 18, 9999.99, Employee.Status.FREE),
            new Employee(103, "王五", 28, 3333.33, Employee.Status.VOCATION),
            new Employee(104, "赵六", 8, 7777.77, Employee.Status.BUSY),
            new Employee(104, "赵六", 8, 7777.77, Employee.Status.FREE),
            new Employee(104, "赵七", 8, 7777.77, Employee.Status.FREE),
            new Employee(105, "田七", 38, 5555.55, Employee.Status.BUSY)
    );
    
    //3. 终止操作
    /*
        allMatch——检查是否匹配所有元素
        anyMatch——检查是否至少匹配一个元素
        noneMatch——检查是否没有匹配的元素
        findFirst——返回第一个元素
        findAny——返回当前流中的任意元素
        count——返回流中元素的总个数
        max——返回流中最大值
        min——返回流中最小值
     */
    @Test
    public void test1(){
            boolean bl = emps.stream()
                .allMatch((e) -> e.getStatus().equals(Employee.Status.BUSY));
            
            System.out.println(bl);
            
            boolean bl1 = emps.stream()
                .anyMatch((e) -> e.getStatus().equals(Employee.Status.BUSY));
            
            System.out.println(bl1);
            
            boolean bl2 = emps.stream()
                .noneMatch((e) -> e.getStatus().equals(Employee.Status.BUSY));
            
            System.out.println(bl2);
    }
    
    @Test
    public void test2(){
        Optional<Employee> op = emps.stream()
            .sorted((e1, e2) -> Double.compare(e1.getSalary(), e2.getSalary()))
            .findFirst();//有可能为空即封装到Optional里
        
        System.out.println(op.get());
        
        System.out.println("--------------------------------");
        
        Optional<Employee> op2 = emps.parallelStream()
            .filter((e) -> e.getStatus().equals(Employee.Status.FREE))
            .findAny();
        
        System.out.println(op2.get());
    }
    
    @Test
    public void test3(){
        long count = emps.stream()
                         .filter((e) -> e.getStatus().equals(Employee.Status.FREE))
                         .count();
        
        System.out.println(count);
        
        Optional<Double> op = emps.stream()
            .map(Employee::getSalary)
            .max(Double::compare);
        
        System.out.println(op.get());
        
        Optional<Employee> op2 = emps.stream()
            .min((e1, e2) -> Double.compare(e1.getSalary(), e2.getSalary()));
        
        System.out.println(op2.get());
    }
    
    //注意：流进行了终止操作后，不能再次使用
    @Test
    public void test4(){
        Stream<Employee> stream = emps.stream()
         .filter((e) -> e.getStatus().equals(Employee.Status.FREE));
        
        long count = stream.count();
        
        stream.map(Employee::getSalary)
            .max(Double::compare);
    }
}

//collect——将流转换为其他形式。接收一个 Collector接口的实现，用于给Stream中元素做汇总的方法
@Test
public void test3(){
    List<String> list = emps.stream()
        .map(Employee::getName)
        .collect(Collectors.toList());
    
    list.forEach(System.out::println);
    
    System.out.println("----------------------------------");
    
    Set<String> set = emps.stream()
        .map(Employee::getName)
        .collect(Collectors.toSet());
    
    set.forEach(System.out::println);

    System.out.println("----------------------------------");
    
    HashSet<String> hs = emps.stream()
        .map(Employee::getName)
        .collect(Collectors.toCollection(HashSet::new));
    
    hs.forEach(System.out::println);
}

@Test
public void test4(){
    Optional<Double> max = emps.stream()
        .map(Employee::getSalary)
        .collect(Collectors.maxBy(Double::compare));
    
    System.out.println(max.get());
    
    Optional<Employee> op = emps.stream()
        .collect(Collectors.minBy((e1, e2) -> Double.compare(e1.getSalary(), e2.getSalary())));
    
    System.out.println(op.get());
    
    Double sum = emps.stream()
        .collect(Collectors.summingDouble(Employee::getSalary));
    
    System.out.println(sum);
    
    Double avg = emps.stream()
        .collect(Collectors.averagingDouble(Employee::getSalary));
    
    System.out.println(avg);
    
    Long count = emps.stream()
        .collect(Collectors.counting());
    
    System.out.println(count);
    
    System.out.println("--------------------------------------------");
    
    DoubleSummaryStatistics dss = emps.stream()
        .collect(Collectors.summarizingDouble(Employee::getSalary));
    
    System.out.println(dss.getMax());
}

//分组
@Test
public void test5(){
    Map<Employee.Status, List<Employee>> map = emps.stream()
        .collect(Collectors.groupingBy(Employee::getStatus));
    
    System.out.println(map);
}

//多级分组
@Test
public void test6(){
    Map<Employee.Status, Map<String, List<Employee>>> map = emps.stream()
        .collect(Collectors.groupingBy(Employee::getStatus, Collectors.groupingBy((e) -> {
            if(e.getAge() >= 60)
                return "老年";
            else if(e.getAge() >= 35)
                return "中年";
            else
                return "成年";
        })));
    
    System.out.println(map);
}

//分区
@Test
public void test7(){
    Map<Boolean, List<Employee>> map = emps.stream()
        .collect(Collectors.partitioningBy((e) -> e.getSalary() >= 5000));
    
    System.out.println(map);
}

//
@Test
public void test8(){
    String str = emps.stream()
        .map(Employee::getName)
        .collect(Collectors.joining("," , "----", "----"));
    
    System.out.println(str);
}

@Test
public void test9(){
    Optional<Double> sum = emps.stream()
        .map(Employee::getSalary)
        .collect(Collectors.reducing(Double::sum));
    
    System.out.println(sum.get());
}