Java中的字典方法
字典是一个抽象类，代表一个键/值存储库，其操作非常类似于Map。给定键和值，您可以将值存储在Dictionary对象中。一旦存储了值，就可以使用其键检索它。因此，就像映射一样，字典可以看作是键/值对的列表。
以下是字典定义的方法，如下所示-
Enumerationelements()
Returnsanenumerationofthevaluescontainedinthedictionary.
返回包含与键关联的值的对象。如果键不在字典中，则返回空对象。
booleanisEmpty()
Returnstrueifthedictionaryisempty,andreturnsfalseifitcontainsatleastonekey.
返回字典中包含的键的枚举。
Objectput(Objectkey,Objectvalue)
Insertsakeyanditsvalueintothedictionary.Returnsnullifthekeyisnotalreadyinthedictionary;returnsthepreviousvalueassociatedwiththekeyifthekeyisalreadyinthedictionary.
删除键及其值。返回与键关联的值。如果键不在字典中，则返回null。
返回字典中的条目数。
以下是实现Dictionary类的put()和get()方法的示例-
示例
import java.util.*;
public class Demo {
public static void main(String[] args) {
Dictionary dictionary = new Hashtable();
dictionary.put("20", "John");
dictionary.put("40", "Tom");
dictionary.put("60", "Steve");
dictionary.put("80", "Kevin");
dictionary.put("100", "Ryan");
dictionary.put("120", "Tim");
dictionary.put("140", "Jacob");
dictionary.put("160", "David");
System.out.println("Value at key 20 = " + dictionary.get("20"));
System.out.println("Value at key 40 = " + dictionary.get("40"));
System.out.println("Value at key 30 = " + dictionary.get("30"));
System.out.println("Value at key 90 = " + dictionary.get("90"));
}
}输出结果
Value at key 20 = John Value at key 40 = Tom Value at key 30 = null Value at key 90 = null
让我们看看另一个示例，其中我们也使用elements()方法显示Dictionary值-
示例
import java.util.*;
public class Demo {
public static void main(String[] args) {
Dictionary dictionary = new Hashtable();
dictionary.put("20", "John");
dictionary.put("40", "Tom");
dictionary.put("60", "Steve");
dictionary.put("80", "Kevin");
dictionary.put("100", "Ryan");
dictionary.put("120", "Tim");
dictionary.put("140", "Jacob");
dictionary.put("160", "David");
System.out.println("Dictionary Values...");
for (Enumeration i = dictionary.elements(); i.hasMoreElements();) {
System.out.println(i.nextElement());
}
System.out.println("Value at key 20 = " + dictionary.get("20"));
System.out.println("Value at key 40 = " + dictionary.get("40"));
System.out.println("Value at key 30 = " + dictionary.get("30"));
System.out.println("Value at key 90 = " + dictionary.get("90"));
}
}输出结果
Dictionary Values... Tom Jacob Steve Ryan David John Kevin Tim Value at key 20 = John Value at key 40 = Tom Value at key 30 = null Value at key 90 = null