list stream：过滤对象中的元素（filter）并进行排序（sorted）

怼烎@ 2023-03-12 12:22 3阅读 0赞

### 目录 ###

*   *   *  特定要求
         *  按年龄升序
         *  按年龄降序

### 特定要求 ###

采用并行模式<**parallelStream**>从集合中筛选<**filter**>特定班级的学生，并且将该部分特定学生通过年龄<**Comparator.comparing**>来进行排序<**sorted**>，将排序好的学生的ID<**map**>放到一个新的集合中<**collect**>

### 按年龄升序 ###

package com.example.starter;
    
    import java.util.ArrayList;
    import java.util.Comparator;
    import java.util.List;
    import java.util.stream.Collectors;
    
    public class TestStream { 
      public static void main(String[] args) { 
    
        List<User> userList = new ArrayList<>();
        User userOne = new User();
        userOne.setId(1L);
        userOne.setAge(5);
        userOne.setClasses("3年2班");
    
        User userTwo = new User();
        userTwo.setId(2L);
        userTwo.setAge(10);
        userTwo.setClasses("4年3班");
    
        User userThree = new User();
        userThree.setId(3L);
        userThree.setAge(8);
        userThree.setClasses("3年2班");
    
        User userFour = new User();
        userFour.setId(4L);
        userFour.setAge(6);
        userFour.setClasses("3年2班");
    
        userList.add(userOne);
        userList.add(userTwo);
        userList.add(userThree);
        userList.add(userFour);
    
        List<Long> userIdList = userList.parallelStream().filter(u -> "3年2班".equals(u.getClasses())).sorted(Comparator.comparing(User::getAge)).map(User::getId).collect(Collectors.toList());
        System.out.println("升序 : " + userIdList);
    
    
      }
    
    
    
    }
    class User { 
      //ID
      private Long id;
      //年龄
      private int age;
      //班级
      private String classes;
    
      public Long getId() { 
        return id;
      }
    
      public void setId(Long id) { 
        this.id = id;
      }
    
      public int getAge() { 
        return age;
      }
    
      public void setAge(int age) { 
        this.age = age;
      }
    
      public String getClasses() { 
        return classes;
      }
    
      public void setClasses(String classes) { 
        this.classes = classes;
      }
    }

### 按年龄降序 ###

package com.example.starter;
    
    import java.util.ArrayList;
    import java.util.Comparator;
    import java.util.List;
    import java.util.stream.Collectors;
    
    public class TestStream { 
      public static void main(String[] args) { 
    
        List<User> userList = new ArrayList<>();
        User userOne = new User();
        userOne.setId(1L);
        userOne.setAge(5);
        userOne.setClasses("3年2班");
    
        User userTwo = new User();
        userTwo.setId(2L);
        userTwo.setAge(10);
        userTwo.setClasses("4年3班");
    
        User userThree = new User();
        userThree.setId(3L);
        userThree.setAge(8);
        userThree.setClasses("3年2班");
    
        User userFour = new User();
        userFour.setId(4L);
        userFour.setAge(6);
        userFour.setClasses("3年2班");
    
        userList.add(userOne);
        userList.add(userTwo);
        userList.add(userThree);
        userList.add(userFour);
    
        List<Long> userIdList = userList.parallelStream().filter(u -> "3年2班".equals(u.getClasses())).sorted(Comparator.comparing(User::getAge).reversed()).map(User::getId).collect(Collectors.toList());
        System.out.println("降序 : " + userIdList);
    
    
      }
    
    
    
    }
    class User { 
      //ID
      private Long id;
      //年龄
      private int age;
      //班级
      private String classes;
    
      public Long getId() { 
        return id;
      }
    
      public void setId(Long id) { 
        this.id = id;
      }
    
      public int getAge() { 
        return age;
      }
    
      public void setAge(int age) { 
        this.age = age;
      }
    
      public String getClasses() { 
        return classes;
      }
    
      public void setClasses(String classes) { 
        this.classes = classes;
      }
    }