Java面试题每日10问(24)

左手的ㄟ右手 2023-09-23 23:19 135阅读 0赞

> # `Java Collections` Interview Questions #

# 1. What is the advantage of Properties file? #

*  If you change the value in the properties file, you don’t need to recompile the java class.
 *  So, it makes the application easy to manage. It is used to store information which is to be changed frequently.

public class Test2 {
        
        public static void main(String[] args) throws Exception {
        
            Properties p = new Properties();
            FileReader in=new FileReader("C:\\PracticeCoding\\bean.properties");
            p.load(in);
            //获取配置文件中的信息
            System.out.println(p.getProperty("user"));
            System.out.println(p.getProperty("password"));
        }
    }

//bean.properties
    user = system
    password = 123456

system
    123456

# 2.What does the hashCode() method? #

*  The hashCode() method returns a hash code value (an integer number).
 *  The hashCode() method returns the same integer number if two keys (by calling equals() method) are identical.
 *  it is possible that two hash code numbers can have different or the same keys.
 *  If two objects do not produce an equal result by using the equals() method, then the hashcode() method will provide the different integer result for both the objects.

# 3.Why we override equals() method? #

*  The equals method is used to check whether two objects are the same or not.
 *  It needs to be overridden if we want to check the objects based on the property.

# 4.How to synchronize List, Set and Map elements? #

Yes, Collections class provides methods to make List, Set or Map elements as synchronized

<table> 
 <thead> 
  <tr> 
   <th>public static List synchronizedList(List l){}</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>public static Set synchronizedSet(Set s){}</td> 
  </tr> 
  <tr> 
   <td>public static SortedSet synchronizedSortedSet(SortedSet s){}</td> 
  </tr> 
  <tr> 
   <td>public static Map synchronizedMap(Map m){}</td> 
  </tr> 
  <tr> 
   <td>public static SortedMap synchronizedSortedMap(SortedMap m){}</td> 
  </tr> 
 </tbody> 
</table>

# 5.What is the advantage of the generic collection? #

*  If we use the generic class, we don’t need typecasting.
 *  It is type-safe and checked at compile time.
 *  Generic confirms the stability of the code by making it bug detectable at compile time.

# 6.What is hash-collision in Hashtable and how it is handled in Java? #

*  Two different keys with the same hash value are known as hash-collision.
 *  Two separate entries will be kept in a single hash bucket to avoid the collision.
 *  There are two ways to **avoid hash-collision**.
    
     *  Separate Chaining
     *  Open Addressing

# 7.What is the Dictionary class? #

*  The Dictionary class provides the capability to store key-value pairs.

# 8.What is the default size of load factor in hashing based collection? #

*  The default size of load factor is 0.75. The default capacity is computed as initial capacity \* `load factor`.
 *  For example, 16 \* 0.75 = 12. So, 12 is the default capacity of Map.

# 9.What do you understand by fail-fast? #

*  The Iterator in java which immediately throws `ConcurrentmodificationException`
 *  if any structural modification occurs in, is called as a `Fail-fast iterator`.
 *  Fail-fast iterator does not require any extra space in memory.

# 10.What is the difference between Array and ArrayList? #

<table> 
 <thead> 
  <tr> 
   <th>Array</th> 
   <th>ArrayList</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>The Array is of fixed size, means we cannot resize the array as per need.</td> 
   <td>ArrayList is not of the fixed size we can change the size dynamically.</td> 
  </tr> 
  <tr> 
   <td>Arrays are of the static type.</td> 
   <td>ArrayList is of dynamic size.</td> 
  </tr> 
  <tr> 
   <td>Arrays can store primitive data types as well as objects.</td> 
   <td>ArrayList cannot store the primitive data types it can only store the objects.</td> 
  </tr> 
 </tbody> 
</table>