如何在Java HashMap中使用空值作为键
是的，您可以在JavaHashMap中将null设置为键。为此，让我们首先创建具有键和值对的HashMap-
Map<String,String>map = new HashMap<>();
map.put("Football", "A");
map.put("Squash", "B");
map.put("Cricket", "C");
map.put("Hockey", "D");
map.put("Rugby", "E");现在，让我们添加空值作为键-
map.put(null, "H");
您可以尝试将键的值获取为“null”-
map.get(null);
示例
import java.util.HashMap;
import java.util.Map;
public class Demo {
public static final void main(String[] args) {
Map<String,String>map = new HashMap<>();
map.put("Football", "A");
map.put("Squash", "B");
map.put("Cricket", "C");
map.put("Hockey", "D");
map.put("Rugby", "E");
map.put("Golf", "F");
map.put("Archery", "G");
System.out.println("Size of HashMap = " + map.size());
map.put(null, "H");
System.out.println("Updated Size of HashMap = " + map.size());
System.out.println("For null = " + map.get(null));
}
}输出结果
Size of HashMap = 7 Updated Size of HashMap = 8 For null = H