Java HashSet isEmpty()方法
Java HashSet isEmpty()方法
Java HashSet类的
isEmpty()方法用于检查是否HashSet包含元素。如果集合包含元素，则返回true，否则返回false。
语法
以下是
isEmpty()方法的声明:
参数
此方法不接受任何参数。
返回
isEmpty()方法如果该集合不包含任何元素，则返回true。
异常
NA
兼容性版本
Java 1.2及更高版本
示例1
import java.util.*;
public class HashSetIsEmptyExample1 {
public static void main(String[] args) {
HashSet<String> hset = new HashSet<String>();
hset.add("Welcome");
hset.add("To");
hset.add("lidihuo");
System.out.println("HashSet Elements: "+hset);
System.out.println("Is the set empty: "+hset.isEmpty());
hset.clear();
System.out.println("Is the set empty: "+hset.isEmpty());
}
}
输出:
HashSet Elements: [Welcome, To, lidihuo]
Is the set empty: false
Is the set empty: true
示例2
import java.util.*;
public class HashSetIsEmptyExample2 {
public static void main(String[] args) {
HashSet <Integer> hashSetObject = new HashSet <>();
hashSetObject.add(45);
hashSetObject.add(67);
hashSetObject.add(98);
boolean b1 = hashSetObject.isEmpty();
System.out.println("Is hash set empty?:- "+b1);
System.out.println("HashSet Element: "+hashSetObject);
hashSetObject.clear();
boolean b2 = hashSetObject.isEmpty();
System.out.println("Is hash set empty?:- "+b2);
System.out.println("HashSet Element: "+hashSetObject);
}
}
输出:
Is hash set empty?:- false
HashSet Element: [98, 67, 45]
Is hash set empty?:- true
HashSet Element: []
示例3
import java.util.*;
public class HashSetIsEmptyExample3 {
public static void main(String[] args) {
HashSet studentSet = init();
if(studentSet.isEmpty()){
System.out.println("student database is empty: "+studentSet);
}
else{
System.out.println("student database has "+studentSet.size()+" names: "+studentSet);
}
studentSet.clear();
if(studentSet.isEmpty()){
System.out.println("student database is empty: "+studentSet);
}
else{
System.out.println("student database has "+studentSet.size()+" names: "+studentSet);
}
}
private static HashSet init() {
HashSet<String> studentSet = new HashSet<>();
studentSet.add("Rahul");
studentSet.add("Mohan");
studentSet.add("Karan");
return studentSet;
}
}
输出:
student database has 3 names: [Rahul, Mohan, Karan]
student database is empty: []
