Java中的字典 isEmpty() 方法

Dictionary 类的isEmpty()方法检查这个字典是否有任何键值映射。仅当此字典中没有条目时，该函数才返回TRUE 。

句法：

public abstract boolean isEmpty()

返回值：如果字典为空，则函数返回TRUE ，否则返回FALSE 。

异常：函数不抛出异常。

下面的程序说明了Dictionary.isEmpty()方法的使用：

方案一：

// Java Program to illustrate
// Dictionary.isEmpty() method
  
import java.util.*;
  
class GFG {
    public static void main(String[] args)
    {
  
        // Create a new hashtable
        Dictionary
            d = new Hashtable();
  
        // 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

方案二：

// Java Program to illustrate
// Dictionary.isEmpty() method
  
import java.util.*;
  
class GFG {
    public static void main(String[] args)
    {
  
        // Create a new hashtable
        Dictionary
            d = new Hashtable();
  
        // 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: Java/util/Dictionary.html#isEmpty()