Java 中的字典 isEmpty()方法
原文:https://www . geesforgeks . org/dictionary-isempty-method-in-Java/
字典类的 isEmpty() 方法检查这个字典是否有键值映射。只有当本词典中没有条目时,该功能才返回真。
语法:
public abstract boolean isEmpty()
返回值:如果字典为空,则函数返回真,否则返回假。
异常:函数没有抛出异常。
以下程序说明了字典的使用方法:
程序 1:
// Java Program to illustrate
// Dictionary.isEmpty() method
import java.util.*;
class GFG {
public static void main(String[] args)
{
// Create a new hashtable
Dictionary<Integer, String>
d = new Hashtable<Integer, String>();
// Insert elements in the hashtable
d.put(1, "Geeks");
d.put(2, "for");
d.put(3, "Geeks");
// Print the Dictionary
System.out.println("\nDictionary: " + d);
// check if this dictionary is empty
// using isEmpty() method
if (d.isEmpty()) {
System.out.println("Dictionary "
+ "is empty");
}
else
System.out.println("Dictionary "
+ "is not empty");
}
}
输出:
Dictionary: {3=Geeks, 2=for, 1=Geeks}
Dictionary is not empty
程序二:
// Java Program to illustrate
// Dictionary.isEmpty() method
import java.util.*;
class GFG {
public static void main(String[] args)
{
// Create a new hashtable
Dictionary<String, String>
d = new Hashtable<String, String>();
// Print the Dictionary
System.out.println("\nDictionary: " + d);
// check if this dictionary is empty
// using isEmpty() method
if (d.isEmpty()) {
System.out.println("Dictionary "
+ "is empty");
}
else
System.out.println("Dictionary "
+ "is not empty");
// Insert elements in the hashtable
d.put("a", "GFG");
d.put("b", "gfg");
// Print the Dictionary
System.out.println("\nDictionary: " + d);
// check if this dictionary is empty
// using isEmpty() method
if (d.isEmpty()) {
System.out.println("Dictionary "
+ "is empty");
}
else
System.out.println("Dictionary "
+ "is not empty");
// Remove elements in the hashtable
d.remove("a");
d.remove("b");
// Print the Dictionary
System.out.println("\nDictionary: " + d);
// check if this dictionary is empty
// using isEmpty() method
if (d.isEmpty()) {
System.out.println("Dictionary "
+ "is empty");
}
else
System.out.println("Dictionary "
+ "is not empty");
}
}
输出:
Dictionary: {}
Dictionary is empty
Dictionary: {b=gfg, a=GFG}
Dictionary is not empty
Dictionary: {}
Dictionary is empty
参考:https://docs . Oracle . com/javase/7/docs/API/Java/util/dictionary . html # isEmpty()
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