Carane nggunakake cara keySet ing java.util.Map

Yen sampeyan perlu kanggo njaluk kabeh tombol sing Peta ngandhut, sampeyan bisa nggunakake cara java.util.HashMap.keySet () tenan Handy . Ing artikel iki, kita bakal nerangake cara kerjane. Sing ngerti, kelas HashMap ngleksanakake antarmuka Map , supaya ing conto kita bakal nggunakake cara HashMap keySet () .

Tanda tangan metode HashMap keySet() lan prinsip operasi

Set<K> metode keySet() ngasilake tampilan Set tombol sing ana ing peta iki. Fitur koleksi Set iki, sing nyimpen tombol, ora ana unsur duplikat. Set kasebut didhukung dening peta. Tegese yen ana sing diganti ing peta, bakal dibayangke ing set kasebut, lan kosok balene. Contone, sampeyan bisa mbusak item saka pesawat iki, lan tombol lan nilai sing cocog otomatis dibusak saka peta, nanging sampeyan ora bisa nambah item anyar ing.

HashMap keySet () conto

Ayo nggawe HashMap kanthi jeneng kanca lan kunci digital banjur nyetak Set tombol nggunakake metode HashMap keySet () .

import java.util.HashMap;
import java.util.Map;
import java.util.Set;

public class KeySetDemo {
   public static void main(String[] args) {
       Map<Integer, String> myHashMap = new HashMap<>();
       myHashMap.put(1, "John");
       myHashMap.put(2, "Ivy");
       myHashMap.put(3, "Ricky");
       myHashMap.put(4, "Andrew");
       myHashMap.put(5, "Alex");

       //using map.keyset() method and print out the result
       Set<Integer> myKeySet = myHashMap.keySet();
       System.out.println("myKeySet of the map: "+myKeySet);

Output yaiku: Kejabi cara java.util.HashMap.keySet () ing Jawa ana cara entrySet () , uga ngasilake Set , nanging pesawat iki ngemot pasangan kunci-nilai. Iki conto karo metode java.util.HashMap.keySet() lan java.util.HashMap.entrySet() :

import java.util.HashMap;
import java.util.Map;
import java.util.Set;

public class KeySetDemo {
   public static void main(String[] args) {
       Map<Integer, String> myHashMap = new HashMap<>();
       myHashMap.put(1, "John");
       myHashMap.put(2, "Ivy");
       myHashMap.put(3, "Ricky");
       myHashMap.put(4, "Andrew");
       myHashMap.put(5, "Alex");

       //using map.keyset() method and print out the result
       Set<Integer> myKeySet = myHashMap.keySet();
       System.out.println("keys of the map: " + myKeySet);
       System.out.println("keys and values of the map: " );
       for( Map.Entry e : myHashMap.entrySet()){
           System.out.println(e.getKey() + " : " + e.getValue());
       }
   }
}

Punika output: Saiki ayo nyoba mbusak unsur saka keySet lan priksa manawa bakal mengaruhi HashMap asli kita .

import java.util.HashMap;
import java.util.Map;
import java.util.Set;

public class KeySetDemo {
   public static void main(String[] args) {
       Map<Integer, String> myHashMap = new HashMap<>();
       myHashMap.put(1, "John");
       myHashMap.put(2, "Ivy");
       myHashMap.put(3, "Ricky");
       myHashMap.put(4, "Andrew");
       myHashMap.put(5, "Alex");

       //using map.keyset() method and print out the result
       Set<Integer> myKeySet = myHashMap.keySet();
       System.out.println("keys of the map: " + myKeySet);
      myKeySet.remove(4);
       System.out.println("myHashMap after removing an element from myKeySet: " + myHashMap);
       System.out.println("keys of the map: " + myKeySet);
   }
}

Output yaiku: Nalika sampeyan bisa ndeleng, kita dibusak tombol "4" saka Set , lan asil njabut pasangan "4-Alex" saka HashMap . Saiki ayo nyoba nambah kunci menyang keySet() :

import java.util.HashMap;
       import java.util.Map;
       import java.util.Set;

public class KeySetDemo {
   public static void main(String[] args) {
       Map<Integer, String> myHashMap = new HashMap<>();
       myHashMap.put(1, "John");
       myHashMap.put(2, "Ivy");
       myHashMap.put(3, "Ricky");
       myHashMap.put(4, "Andrew");
       myHashMap.put(5, "Alex");

       //using map.keyset() method and print out the result
       Set<Integer> myKeySet = myHashMap.keySet();
       System.out.println("keys of the map: " + myKeySet);
       myKeySet.add(7);

   }
}

Ing kasus iki, kita bakal entuk Pengecualian, amarga keySet kita disambungake menyang hashMap :