Java 开发 - 含有 null 值字段的对象排序（自定义 Comparator、使用 Comparator、使用 Stream API）

我命由我123452025-12-30 8:11

准备阶段

  • Student.java
java 复制代码 
public class Student {
    private Integer id;
    private String name;

    public Student(Integer id, String name) {
        this.id = id;
        this.name = name;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
}

基础排序

  1. 升序排序
java 复制代码 
List<Student> list = new ArrayList<>();

list.add(new Student(1001, "张三"));
list.add(new Student(1003, "王五"));
list.add(new Student(1002, "李四"));

list.sort(Comparator.comparingInt(Student::getId));

System.out.println(list);
复制代码 
# 输出结果

[Student{id=1001, name='张三'}, Student{id=1002, name='李四'}, Student{id=1003, name='王五'}]
  1. 降序排序
java 复制代码 
List<Student> list = new ArrayList<>();

list.add(new Student(1001, "张三"));
list.add(new Student(1003, "王五"));
list.add(new Student(1002, "李四"));

list.sort((o1, o2) -> o2.getId() - o1.getId());

System.out.println(list);
复制代码 
# 输出结果

[Student{id=1003, name='王五'}, Student{id=1002, name='李四'}, Student{id=1001, name='张三'}]

含有 null 值字段的对象排序

1、自定义 Comparator
  1. 升序排序，含有 null 值字段的对象放在最后面
java 复制代码 
List<Student> list = new ArrayList<>();

list.add(new Student(1001, "张三"));
list.add(new Student(null, "王五"));
list.add(new Student(1002, "李四"));
list.add(new Student(null, "赵六"));
list.add(new Student(1005, "孙七"));

list.sort((o1, o2) -> {
    Integer id1 = o1.getId();
    Integer id2 = o2.getId();

    if (id1 == null && id2 == null) {
        return 0;
    }
    if (id1 == null) {
        return 1;
    }
    if (id2 == null) {
        return -1;
    }
    return id1 - id2;
});

System.out.println(list);
复制代码 
# 输出结果

[Student{id=1001, name='张三'}, Student{id=1002, name='李四'}, Student{id=1005, name='孙七'}, Student{id=null, name='王五'}, Student{id=null, name='赵六'}]
  1. 降序排序，含有 null 值字段的对象放在最后面
java 复制代码 
List<Student> list = new ArrayList<>();

list.add(new Student(1001, "张三"));
list.add(new Student(null, "王五"));
list.add(new Student(1002, "李四"));
list.add(new Student(null, "赵六"));
list.add(new Student(1005, "孙七"));

list.sort((o1, o2) -> {
    Integer id1 = o1.getId();
    Integer id2 = o2.getId();

    if (id1 == null && id2 == null) {
        return 0;
    }
    if (id1 == null) {
        return 1;
    }
    if (id2 == null) {
        return -1;
    }
    return id2 - id1;
});

System.out.println(list);
复制代码 
# 输出结果

[Student{id=1005, name='孙七'}, Student{id=1002, name='李四'}, Student{id=1001, name='张三'}, Student{id=null, name='王五'}, Student{id=null, name='赵六'}]
  1. 升序排序，含有 null 值字段的对象放在最前面
java 复制代码 
List<Student> list = new ArrayList<>();

list.add(new Student(1001, "张三"));
list.add(new Student(null, "王五"));
list.add(new Student(1002, "李四"));
list.add(new Student(null, "赵六"));
list.add(new Student(1005, "孙七"));

list.sort((o1, o2) -> {
    Integer id1 = o1.getId();
    Integer id2 = o2.getId();

    if (id1 == null && id2 == null) {
        return 0;
    }
    if (id1 == null) {
        return -1;
    }
    if (id2 == null) {
        return 1;
    }
    return id1 - id2;
});

System.out.println(list);
复制代码 
# 输出结果

[Student{id=null, name='王五'}, Student{id=null, name='赵六'}, Student{id=1001, name='张三'}, Student{id=1002, name='李四'}, Student{id=1005, name='孙七'}]
  1. 降序排序，含有 null 值字段的对象放在最前面
java 复制代码 
List<Student> list = new ArrayList<>();

list.add(new Student(1001, "张三"));
list.add(new Student(null, "王五"));
list.add(new Student(1002, "李四"));
list.add(new Student(null, "赵六"));
list.add(new Student(1005, "孙七"));

list.sort((o1, o2) -> {
    Integer id1 = o1.getId();
    Integer id2 = o2.getId();

    if (id1 == null && id2 == null) {
        return 0;
    }
    if (id1 == null) {
        return -1;
    }
    if (id2 == null) {
        return 1;
    }
    return id2 - id1;
});

System.out.println(list);
复制代码 
# 输出结果

[Student{id=null, name='王五'}, Student{id=null, name='赵六'}, Student{id=1005, name='孙七'}, Student{id=1002, name='李四'}, Student{id=1001, name='张三'}]
2、使用 Comparator
  1. 升序排序，含有 null 值字段的对象放在最后面
java 复制代码 
List<Student> list = new ArrayList<>();

list.add(new Student(1001, "张三"));
list.add(new Student(null, "王五"));
list.add(new Student(1002, "李四"));
list.add(new Student(null, "赵六"));
list.add(new Student(1005, "孙七"));

list.sort(
        Comparator.comparing(
                Student::getId,
                Comparator.nullsLast(Comparator.naturalOrder())
        )
);

System.out.println(list);
复制代码 
# 输出结果

[Student{id=1001, name='张三'}, Student{id=1002, name='李四'}, Student{id=1005, name='孙七'}, Student{id=null, name='王五'}, Student{id=null, name='赵六'}]
  1. 降序排序，含有 null 值字段的对象放在最后面
java 复制代码 
List<Student> list = new ArrayList<>();

list.add(new Student(1001, "张三"));
list.add(new Student(null, "王五"));
list.add(new Student(1002, "李四"));
list.add(new Student(null, "赵六"));
list.add(new Student(1005, "孙七"));

list.sort(
        Comparator.comparing(
                Student::getId,
                Comparator.nullsLast(Comparator.reverseOrder())
        )
);

System.out.println(list);
复制代码 
# 输出结果

[Student{id=1005, name='孙七'}, Student{id=1002, name='李四'}, Student{id=1001, name='张三'}, Student{id=null, name='王五'}, Student{id=null, name='赵六'}]
  1. 升序排序，含有 null 值字段的对象放在最前面
java 复制代码 
List<Student> list = new ArrayList<>();

list.add(new Student(1001, "张三"));
list.add(new Student(null, "王五"));
list.add(new Student(1002, "李四"));
list.add(new Student(null, "赵六"));
list.add(new Student(1005, "孙七"));

list.sort(
        Comparator.comparing(
                Student::getId,
                Comparator.nullsFirst(Comparator.naturalOrder())
        )
);

System.out.println(list);
复制代码 
# 输出结果

[Student{id=null, name='王五'}, Student{id=null, name='赵六'}, Student{id=1001, name='张三'}, Student{id=1002, name='李四'}, Student{id=1005, name='孙七'}]
  1. 降序排序，含有 null 值字段的对象放在最前面
java 复制代码 
List<Student> list = new ArrayList<>();

list.add(new Student(1001, "张三"));
list.add(new Student(null, "王五"));
list.add(new Student(1002, "李四"));
list.add(new Student(null, "赵六"));
list.add(new Student(1005, "孙七"));

list.sort(
        Comparator.comparing(
                Student::getId,
                Comparator.nullsFirst(Comparator.reverseOrder())
        )
);

System.out.println(list);
复制代码 
# 输出结果

[Student{id=null, name='王五'}, Student{id=null, name='赵六'}, Student{id=1005, name='孙七'}, Student{id=1002, name='李四'}, Student{id=1001, name='张三'}]
3、使用 Stream API
  1. 升序排序，含有 null 值字段的对象放在最后面
java 复制代码 
List<Student> list = new ArrayList<>();

list.add(new Student(1001, "张三"));
list.add(new Student(null, "王五"));
list.add(new Student(1002, "李四"));
list.add(new Student(null, "赵六"));
list.add(new Student(1005, "孙七"));

List<Student> sortedList = list.stream()
        .sorted(Comparator.comparing(
                Student::getId,
                Comparator.nullsLast(Comparator.naturalOrder())
        ))
        .collect(Collectors.toList());

System.out.println(sortedList);
复制代码 
# 输出结果

[Student{id=1001, name='张三'}, Student{id=1002, name='李四'}, Student{id=1005, name='孙七'}, Student{id=null, name='王五'}, Student{id=null, name='赵六'}]
  1. 降序排序，含有 null 值字段的对象放在最后面
java 复制代码 
List<Student> list = new ArrayList<>();

list.add(new Student(1001, "张三"));
list.add(new Student(null, "王五"));
list.add(new Student(1002, "李四"));
list.add(new Student(null, "赵六"));
list.add(new Student(1005, "孙七"));

List<Student> sortedList = list.stream()
        .sorted(Comparator.comparing(
                Student::getId,
                Comparator.nullsLast(Comparator.reverseOrder())
        ))
        .collect(Collectors.toList());

System.out.println(sortedList);
复制代码 
# 输出结果

[Student{id=1005, name='孙七'}, Student{id=1002, name='李四'}, Student{id=1001, name='张三'}, Student{id=null, name='王五'}, Student{id=null, name='赵六'}]
  1. 升序排序，含有 null 值字段的对象放在最前面
java 复制代码 
List<Student> list = new ArrayList<>();

list.add(new Student(1001, "张三"));
list.add(new Student(null, "王五"));
list.add(new Student(1002, "李四"));
list.add(new Student(null, "赵六"));
list.add(new Student(1005, "孙七"));

List<Student> sortedList = list.stream()
        .sorted(Comparator.comparing(
                Student::getId,
                Comparator.nullsFirst(Comparator.naturalOrder())
        ))
        .collect(Collectors.toList());

System.out.println(sortedList);
复制代码 
# 输出结果

[Student{id=null, name='王五'}, Student{id=null, name='赵六'}, Student{id=1001, name='张三'}, Student{id=1002, name='李四'}, Student{id=1005, name='孙七'}]
  1. 降序排序，含有 null 值字段的对象放在最前面
java 复制代码 
List<Student> list = new ArrayList<>();

list.add(new Student(1001, "张三"));
list.add(new Student(null, "王五"));
list.add(new Student(1002, "李四"));
list.add(new Student(null, "赵六"));
list.add(new Student(1005, "孙七"));

List<Student> sortedList = list.stream()
        .sorted(Comparator.comparing(
                Student::getId,
                Comparator.nullsFirst(Comparator.reverseOrder())
        ))
        .collect(Collectors.toList());

System.out.println(sortedList);
复制代码 
# 输出结果

[Student{id=null, name='王五'}, Student{id=null, name='赵六'}, Student{id=1005, name='孙七'}, Student{id=1002, name='李四'}, Student{id=1001, name='张三'}]
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