HashMap trong Java

BแปŸi: James Hartman James Hartman
Hours cแบญp nhแบญt

Hashmap trong ฤ‘รณ lร  gรฌ Java?

HashMap vแป cฦก bแบฃn chแป‰ ฤ‘แป‹nh chรฌa khรณa duy nhแบฅt tฦฐฦกng แปฉng giรก trแป‹ cรณ thแปƒ ฤ‘ฦฐแปฃc lแบฅy ra tแบกi bแบฅt kแปณ ฤ‘iแปƒm nร o.

HashMap trong Java

ฤแบทc ฤ‘iแปƒm cแปงa Java Bแบฃn ฤ‘แป“ bฤƒm

a) Cรกi giรก trแป‹ cรณ thแปƒ ฤ‘ฦฐแปฃc lฦฐu trแปฏ trong bแบฃn ฤ‘แป“ bแบฑng cรกch hรฌnh thร nh mแป™t giรก trแป‹ cแป‘t lรตi ฤ‘รดi. Giรก trแป‹ cรณ thแปƒ ฤ‘ฦฐแปฃc lแบฅy bแบฑng cรกch sแปญ dแปฅng khรณa bแบฑng cรกch chuyแปƒn nรณ ฤ‘แบฟn phฦฐฦกng thแปฉc chรญnh xรกc.

b) Nแบฟu khรดng cรณ phแบงn tแปญ tแป“n tแบกi trong Bแบฃn ฤ‘แป“, nรณ sแบฝ nรฉm ra mแป™t 'NoSuchElementException'.

c) Chแป‰ lฦฐu trแปฏ HashMap tร i liแป‡u tham khแบฃo ฤ‘แป‘i tฦฐแปฃng. Chรญnh vรฌ thแบฟ, khรดng thแปƒ sแปญ dแปฅng kiแปƒu dแปฏ liแป‡u nguyรชn thแปงy nhฦฐ double hoแบทc int. Sแปญ dแปฅng lแป›p wrapper (nhฦฐ Integer hoแบทc Double) thay thแบฟ.

ฤแบทc ฤ‘iแปƒm cแปงa Java Bแบฃn ฤ‘แป“ bฤƒm

Sแปญ dแปฅng HashMaps trong Java Chฦฐฦกng trรฌnh:

Sau ฤ‘รขy lร  hai cรกch ฤ‘แปƒ khai bรกo Hash Map:

HashMap<String, Object> map = new HashMap<String, Object>();
HashMap x  = new HashMap();

Cรกc phฦฐฦกng thแปฉc Hashmap quan trแปng

  • nhแบญn ฤ‘ฦฐแปฃc (Khรณa ฤ‘แป‘i tฦฐแปฃng) โ€“ ฤiแปu nร y sแบฝ trแบฃ vแป giรก trแป‹ ฤ‘ฦฐแปฃc liรชn kแบฟt vแป›i mแป™t khรณa ฤ‘ฦฐแปฃc chแป‰ ฤ‘แป‹nh trong nร y Java hashmap.
  • put(Khรณa ฤ‘แป‘i tฦฐแปฃng, Chuแป—i VALUE) โ€“ Phฦฐฦกng thแปฉc nร y lฦฐu trแปฏ giรก trแป‹ ฤ‘ฦฐแปฃc chแป‰ ฤ‘แป‹nh vร  liรชn kแบฟt nรณ vแป›i khรณa ฤ‘ฦฐแปฃc chแป‰ ฤ‘แป‹nh trong bแบฃn ฤ‘แป“ nร y.

Java Vรญ dแปฅ vแป Hashmap

Sau ฤ‘รขy lร  mแป™t vรญ dแปฅ vแป triแปƒn khai Hash Map cแปงa Java:

import java.util.HashMap;
import java.util.Map;
public class Sample_TestMaps{
  public static void main(String[] args){
    Map<String, String> objMap = new HashMap<String, String>();
    objMap.put("Name", "Suzuki");
    objMap.put("Power", "220");
    objMap.put("Type", "2-wheeler");
    objMap.put("Price", "85000");
    System.out.println("Elements of the Map:");
    System.out.println(objMap);
  }
}

ฤแบงu ra:

Elements of the Map:
{Type=2-wheeler, Price=85000, Power=220, Name=Suzuki}

Vรญ dแปฅ: Xรณa giรก trแป‹ khแปi HashMap dแปฑa trรชn khรณa

import java.util.*;  
public class HashMapExample {  
   public static void main(String args[]) {  
   // create and populate hash map  
   HashMap<Integer, String> map = new HashMap<Integer, String>();           
   map.put(1,"Java");  
   map.put(2, "Python");  
   map.put(3, "PHP");  
   map.put(4, "SQL");
   map.put(5, "C++");
   System.out.println("Tutorial in Guru99: "+ map);    
   // Remove value of key 5  
   map.remove(5);  
   System.out.println("Tutorial in Guru99 After Remove: "+ map);
   }
}

ฤแบงu ra:

Tutorial in Guru99: {1=Java, 2=Python, 3=PHP, 4=SQL, 5=C++}
Tutorial in Guru99 After Remove: {1=Java, 2=Python, 3=PHP, 4=SQL}

NHแปฎNG Bร€I VIแบพT LIรŠN QUAN

Hรฃy ฤ‘แปƒ chรบng tรดi hแปi mแป™t sแป‘ truy vแบฅn tแป›i chรญnh Hash Map ฤ‘แปƒ biแบฟt rรต hฦกn vแป nรณ

Hแปi: Vแบญy Mr.Hash Map, lร m cรกch nร o tรดi cรณ thแปƒ biแบฟt liแป‡u mแป™t khรณa cแปฅ thแปƒ ฤ‘รฃ ฤ‘ฦฐแปฃc gรกn cho bแบกn hay chฦฐa?

ฤรกp: Thแบญt tuyแป‡t, bแบกn cรณ thแปƒ sแปญ dแปฅng phฦฐฦกng thแปฉc containsKey(Object KEY) vแป›i tรดi, nรณ sแบฝ trแบฃ vแป giรก trแป‹ Boolean nแบฟu tรดi cรณ giรก trแป‹ cho khรณa ฤ‘รฃ cho.

H: Lร m cรกch nร o ฤ‘แปƒ tรฌm thแบฅy tแบฅt cแบฃ cรกc khรณa cรณ sแบตn trรชn Bแบฃn ฤ‘แป“?

A: Tรดi cรณ mแป™t phฦฐฦกng phรกp gแปi lร  bแป™ chรฌa khoรก() sแบฝ trแบฃ vแป tแบฅt cแบฃ cรกc phรญm trรชn bแบฃn ฤ‘แป“. Trong vรญ dแปฅ trรชn, nแบฟu bแบกn viแบฟt mแป™t dรฒng nhฦฐ โ€“
System.out.println(objMap.keySet());

Nรณ sแบฝ trแบฃ vแป mแป™t ฤ‘แบงu ra nhฦฐ-
[Tรชn, Loแบกi, Cรดng suแบฅt, Giรก]

Tฦฐฦกng tแปฑ, nแบฟu bแบกn chแป‰ cแบงn tแบฅt cแบฃ cรกc giรก trแป‹, tรดi cรณ mแป™t phฦฐฦกng phรกp giรก trแป‹().
System.out.println(objMap.values());

Nรณ sแบฝ trแบฃ vแป mแป™t ฤ‘แบงu ra nhฦฐ-
[Suzuki, xe 2 bรกnh, 220, 85000]

Hแปi: Giแบฃ sแปญ tรดi chแป‰ cแบงn xรณa mแป™t khรณa cแปฅ thแปƒ khแปi Bแบฃn ฤ‘แป“, tรดi cรณ cแบงn xรณa toร n bแป™ Bแบฃn ฤ‘แป“ khรดng?

A: Khรดng ฤ‘รขu anh bแบกn!! Tรดi cรณ mแป™t phฦฐฦกng phรกp tแบฉy(Object KEY) sแบฝ chแป‰ xรณa cแบทp khรณa-giรก trแป‹ cแปฅ thแปƒ ฤ‘รณ.

Cรขu hแปi: Lร m cรกch nร o ฤ‘แปƒ chรบng tรดi cรณ thแปƒ kiแปƒm tra xem bแบกn cรณ thแปฑc sแปฑ chแปฉa mแป™t sแป‘ cแบทp khรณa-giรก trแป‹ hay khรดng?

A: Chแป‰ cแบงn kiแปƒm tra xem tรดi cรณ trแป‘ng hay khรดng thรดi!! Tรณm lแบกi lร  dรนng isEmpty() phฦฐฦกng phรกp chแป‘ng lแบกi tรดi..

Tรณm tแบฏt bร i viแบฟt nร y vแป›i: