如何在 Java 中给 TreeSet 添加自定义类对象？
TreeSet 是 java 中 SortedSet 接口的实现，使用红黑树进行存储。默认情况下，它保持升序。它只包含独特的元素。它不允许空元素。存取和检索时间相当快。要将用户定义的对象添加到 TreeSet 中，我们需要实现一个可比较的接口。我们要在 TreeSet 中添加的元素必须是可比较的类型。如果我们不实现可比接口，那么它将抛出 ClassCastException。
例 1
Java 语言(一种计算机语言，尤用于创建网站)
// Importing util package
import java.util.*;
// Custome class Car implements Comparable interface
class Car implements Comparable<Car> {
// attributes
int Modelno;
String name, city;
int stock;
// Car constructor
public Car(int Modelno, String name, String city,
int stock)
{
this.Modelno = Modelno;
this.name = name;
this.city = city;
this.stock = stock;
}
// Override the compareTo() method
public int compareTo(Car c)
{
if (stock > c.stock) {
return 1;
}
else if (stock < c.stock) {
return -1;
}
else {
return 0;
}
}
}
public class GFG {
// Main driver method
public static void main(String[] args)
{
// Define an objects of TreeSet class
TreeSet<Car> set = new TreeSet<Car>();
// Creating Car objects
Car c1 = new Car(132, "BMW", "Rajkot", 35);
Car c2 = new Car(269, "Audi", "Surat", 20);
Car c3 = new Car(560, "Kia", "Vadodara", 15);
Car c4 = new Car(109, "Creta", "Ahmedabad", 26);
// Adding Car objects to TreeSet
set.add(c1);
set.add(c2);
set.add(c3);
set.add(c4);
// Traversing TreeSet
for (Car c : set) {
System.out.println(c.stock + " " + c.name + " "
+ c.city + " " + c.Modelno);
}
}
}
Output
15 Kia Vadodara 560
20 Audi Surat 269
26 Creta Ahmedabad 109
35 BMW Rajkot 132
我们需要覆盖 compareTo() 方法，这样它就会按照特定的顺序对我们的集合进行排序。
示例 2: 让我们举同一个例子，但是现在我们针对汽车的名称覆盖了 compareTo()方法。
Java 语言(一种计算机语言，尤用于创建网站)
// Importing util package
import java.util.*;
// Custome class Car implements Comparable interface
class Car implements Comparable<Car> {
// attributes
int Modelno;
String name, city;
int stock;
// Car constructor
public Car(int Modelno, String name, String city,
int stock)
{
this.Modelno = Modelno;
this.name = name;
this.city = city;
this.stock = stock;
}
// Override the compareTo() method
public int compareTo(Car c)
{
return name.compareTo(c.name);
}
}
public class GFG {
// Main driver method
public static void main(String[] args)
{
// Define an objects of TreeSet class
TreeSet<Car> set = new TreeSet<Car>();
// Creating Car objects
Car c1 = new Car(132, "BMW", "Rajkot", 35);
Car c2 = new Car(269, "Audi", "Surat", 20);
Car c3 = new Car(560, "Kia", "Vadodara", 15);
Car c4 = new Car(109, "Creta", "Ahmedabad", 26);
// Adding Car objects to TreeSet
set.add(c1);
set.add(c2);
set.add(c3);
set.add(c4);
// Traversing TreeSet
for (Car c : set) {
System.out.println(c.name + " " + c.stock + " "
+ c.city + " " + c.Modelno);
}
}
}
Output
Audi 20 Surat 269
BMW 35 Rajkot 132
Creta 26 Ahmedabad 109
Kia 15 Vadodara 560
版权属于：月萌API www.moonapi.com，转载请注明出处
