程序从HashMap获取键集。
示例
import java.util.Iterator;import java.util.HashMap;import java.util.Set;class HashMapExample{ public static void main(String args[]) { // Create a HashMap HashMap<String, String> hmap = new HashMap<String, String>(); // Adding few elements hmap.put("Key1", "Jack"); hmap.put("Key2", "Rock"); hmap.put("Key3", "Rick"); hmap.put("Key4", "Smith"); hmap.put("Key5", "Will"); // Getting Set of HashMap keys /* public Set<K> keySet(): Returns a Set view of the keys contained * in this map. The set is backed by the map, so changes to the map * are reflected in the set, and vice-versa. */ Set<String> keys = hmap.keySet(); System.out.println("Set of Keys contains: "); /* If your HashMap has integer keys then specify the iterator like * this: Iterator<Integer> it = keys.iterator(); */ Iterator<String> it = keys.iterator(); // Displaying keys. Output will not be in any particular order while(it.hasNext()){ System.out.println(it.next()); } }}
输出：
Set of Keys contains: Key2Key1Key4Key3Key5
注意：这组键由原始HashMap备份，因此如果从Set中删除任何键，它将自动从HashMap中删除。
