Java 中如何使用可比接口对 HashSet 元素进行排序？
原文:https://www . geeksforgeeks . org/how-sort-hashset-elements-使用 java 中的可比接口/
HashSet 类实现了 Set 接口，由哈希表支持，哈希表实际上是一个 HashMap 实例。不能保证集合的迭代顺序，这意味着当我们迭代 HashSet 时，不能保证我们得到的元素是按照它们被插入的顺序。
要使用 java 中的可比接口对 HashSet 元素进行排序，首先，我们创建一个实现可比接口的类 Student。在这个类中，我们覆盖了 compareTo() 方法。
*伪代码:*
// Student class implements comparable interface
class Student implements Comparable<Student> {
Integer marks;
Student(Integer marks) {
this.marks = marks;
}
// override toString method
public String toString() {
return (" " + this.marks);
}
// Override compareTo method to sort LinkedHashSet in ascending order
public int compareTo(Student stu) {
return this.marks.compareTo(stu.marks);
}
}
然后我们将集合传递给 TreeSet 构造函数来对元素进行排序。
// TreeSet to sort LinkedHashSet using comparable
TreeSet<Student> tree_set = new TreeSet<>(set);
*以下是上述方法的全面实施:*
*例 1:*
Java
// Java program to demonstrate how to Sort HashSet using
// Comparable interface
import java.util.*;
// Student class implements comparable interface
class Student implements Comparable<Student> {
Integer marks;
Student(Integer marks) { this.marks = marks; }
// override toString method
public String toString() { return (" " + this.marks); }
// Override compareTo method to sort HashSet in
// ascending order
public int compareTo(Student stu)
{
return this.marks.compareTo(stu.marks);
}
}
class GFG {
public static void main(String[] args)
{
// New HashSet
HashSet<Student> set = new HashSet<>();
// Adding elements to the set
set.add(new Student(500));
set.add(new Student(300));
set.add(new Student(400));
set.add(new Student(100));
set.add(new Student(200));
// Print Before sort
System.out.println("Before sort elements in ascending order : "
+ set);
// TreeSet to sort HashSet using comparable
// interface
TreeSet<Student> tree_set = new TreeSet<>(set);
// Print after sorting
System.out.println("After sort elements in ascending order : "
+ tree_set);
}
}
**输出
Before sort elements in ascending order : [ 300, 400, 500, 200, 100]
After sort elements in ascending order : [ 100, 200, 300, 400, 500]
```**
****例 2:****
## **Java**
```java
// Java program to demonstrate how to Sort HashSet using
// Comparable interface
import java.util.*;
// Student class implements comparable interface
class Student implements Comparable<Student> {
Integer marks;
Student(Integer marks) { this.marks = marks; }
// override toString method
public String toString() { return (" " + this.marks); }
// Override compareTo method to sort HashSet in
// descending order
public int compareTo(Student stu)
{
return stu.marks.compareTo(this.marks);
}
}
class GFG {
public static void main(String[] args)
{
// New HashSet
HashSet<Student> set = new HashSet<>();
// Adding elements to the set
set.add(new Student(500));
set.add(new Student(300));
set.add(new Student(400));
set.add(new Student(100));
set.add(new Student(200));
// Print Before sort
System.out.println("Before sort elements in descending order : "
+ set);
// TreeSet to sort HashSet using comparable
// interface
TreeSet<Student> tree_set = new TreeSet<>(set);
// Print after sorting
System.out.println("After sort elements in descending order : "
+ tree_set);
}
}
**输出
java
Before sort elements in descending order : [ 300, 400, 500, 200, 100]
After sort elements in descending order : [ 500, 400, 300, 200, 100]**
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