Java8中Stream的排序，查找和匹配的用法

排序

1. sorted( )---自然排序

2. sorted(Comparator com)---定制排序

   

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   public class Employee {
   
   private String name;
   private Integer age;
   private Double salary;
   private Status status;
   
   public Employee() {
       super();
   }
   
   public  Employee(Integer age){
       this.age = age;
   }
   
   public Employee(String name, Integer age, Double salary) {
       super();
       this.name = name;
       this.age = age;
       this.salary = salary;
   }
   
   public Employee(String name, Integer age, Double salary, Status status) {
       this.name = name;
       this.age = age;
       this.salary = salary;
       this.status = status;
   }
   
   public String getName() {
       return name;
   }
   
   public void setName(String name) {
       this.name = name;
   }
   
   public int getAge() {
       return age;
   }
   
   public void setAge(Integer age) {
       this.age = age;
   }
   
   public double getSalary() {
       return salary;
   }
   
   public void setSalary(Double salary) {
       this.salary = salary;
   }
   
   public Status getStatus() {
       return status;
   }
   
   public void setStatus(Status status) {
       this.status = status;
   }
   
   @Override
   public String toString() {
       return "Employee{" +
               "name='" + name + '\'' +
               ", age=" + age +
               ", salary=" + salary +
               ", status=" + status +
               '}';
   }
   
   @Override
   public boolean equals(Object o) {
       if (this == o) return true;
       if (o == null || getClass() != o.getClass()) return false;
       Employee employee = (Employee) o;
       return age == employee.age &&
               Double.compare(employee.salary, salary) == 0 &&
               Objects.equals(name, employee.name);
   }
   
   @Override
   public int hashCode() {
       return Objects.hash(name, age, salary);
   }
   
   public enum Status{
       FREE,
       BUSY,
       VOCATION;
   }
   }

   @Test
   public void test1(){
       List list = Arrays.asList("ccc", "aaa", "bbb", "ddd", "eee");
   
       //自然排序
       list.stream()
           .sorted()
           .forEach(System.out::println);
   
       System.out.println("------------------------------");
   
       //定制排序
       employees.stream()
                .sorted((e1, e2) -> {
                    if (e1.getAge() == e2.getAge()){
                        return e1.getName().compareTo(e2.getName());
                    }else{
                        return Integer.compare(e1.getAge(), e2.getAge());
                    }
                }).forEach(System.out::println);
   }

   查找與匹配

3. allMatch---檢查是否匹配所有元素
4. anyMatch---檢查是否至少匹配一個元素
5. noneMatch---檢查是否沒有匹配所有元素
6. findFirst---返回第一個元素
7. findAny---返回當(dāng)前流中的任意元素
8. count---返回流中元素的總個數(shù)
9. max---返回流中最大值

10. min---返回流中最小值

    List employees = Arrays.asList(
            new Employee("張三", 18 ,9999.99, Employee.Status.FREE),
            new Employee("李四", 38, 5555.99, Employee.Status.BUSY),
            new Employee("王五", 50, 6666.66, Employee.Status.VOCATION),
            new Employee("趙六", 16, 3333.33, Employee.Status.FREE),
            new Employee("田七", 8, 7777.77, Employee.Status.BUSY)
    );
    @Test
    public void test2(){
        //allMatch---檢查是否匹配所有元素
        boolean b1 = employees.stream()
                .allMatch((e) -> e.getStatus().equals(Employee.Status.BUSY));
        System.out.println(b1);
    
        //anyMatch---檢查是否至少匹配一個元素
        boolean b2 = employees.stream()
                 .anyMatch((e) -> e.getStatus().equals(Employee.Status.BUSY));
        System.out.println(b2);
    
        //noneMatch---檢查是否沒有匹配所有元素
        boolean b3 = employees.stream()
                 .noneMatch((e) -> e.getStatus().equals(Employee.Status.BUSY));
        System.out.println(b3);
    
        //findFirst---返回第一個元素
        Optional op = employees.stream()
                 .sorted((e1, e2) -> Double.compare(e1.getSalary(), e2.getSalary()))
                 .findFirst();
        System.out.println(op.get());
    
        //findAny---返回當(dāng)前流中的任意元素
        Optional op2 = employees.stream()
                 .filter((e) -> e.getStatus().equals(Employee.Status.FREE))
                 .findAny();
        System.out.println(op2.get());
    }
    
    @Test
    public void test3(){
        //count---返回流中元素的總個數(shù)
        Long count = employees.stream()
                 .count();
        System.out.println(count);
    
        //max---返回流中最大值
        Optional op1 = employees.stream()
                .max((e1, e2) -> Double.compare(e1.getSalary(), e2.getSalary()));
        System.out.println(op1.get());
    
        //min---返回流中最小值
        Optional op2 = employees.stream()
                .map(Employee::getSalary)
                .min(Double::compare);
        System.out.println(op2.get());
    }