300+ Java Generics FAQs and Answers [Experienced / Freshers]

Java Generics Interview Questions And Answers

Question: 1. What Are Generics?

Answer:

Generics are used to create Generic Classes and Generic techniques that can paintings with unique Types(Classes).

Question: 2. What Are Advantages Of Using Generics?

Answer:

Advantage of Java Generics:

There are especially 3 advantages of generics. They are as follows:

Type-protection : We can preserve handiest a single type of items in generics. It doesn’t allow to shop other gadgets.

Type casting isn’t required: There isn’t any need to typecast the item.

Before Generics, we need to kind forged.

List list = new ArrayList();  
listing.Add(“hiya”);  
String s = (String) listing.Get(zero);//typecasting  
After Generics, we don’t want to typecast the item.
List listing = new ArrayList();  
listing.Upload(“howdy”);  
String s = list.Get(0);  

Compile-Time Checking: It is checked at compile time so trouble will now not arise at runtime. The suitable programming approach says it is far higher to address the problem at bring together time than runtime.

List list = new ArrayList();  
list.Upload(“hi there”);  
listing.Upload(32);//Compile Time Error  

Adv Java Interview Questions
Question: 3. If The Compiler Erases All Type Parameters At Compile Time, Why Should You Use Generics?

Answer:

You must use generics due to the fact:

The Java compiler enforces tighter type checks on prevalent code at collect time.
Generics guide programming types as parameters.
Generics allow you to put in force widespread algorithms
Question: 4. Write A Generic Method To Exchange The Positions Of Two Different Elements In An Array.

Answer:

public final class Algorithm

    public static void switch(T[] a, int i, int j)

        T temp = a[i];
        a[i] = a[j];
        a[j] = temp;
    

 

Adv Java Tutorial
Question: five. Will The Following Class Compile? If Not, Why?
Public Final Class Algorithm 
Public Static T Max(t X, T Y) 
Return X > Y ? X : Y;

Answer:

No. The extra than (>) operator applies only to primitive numeric kinds.

J2EE Interview Questions
Question: 6. What Is The Following Class Converted To After Type Erasure?
Public Class Pair 

Public Pair(k Key, V Value) 
This.Key = Key;
This.Cost = Value;

Public K Getkey();  Return Key; 
Public V Getvalue();  Return Value; 

Public Void Setkey(k Key)  This.Key = Key; 
Public Void Setvalue(v Value)  This.Fee = Value; 

Private K Key;
Private V Value;

Answer:

public class Pair 
    public Pair(Object key, Object cost) 
        this.Key = key;
        this.Price = cost;
    
    public Object getKey()    go back key; 
    public Object getValue()  return cost; 
    public void setKey(Object key)      this.Key = key; 
    public void setValue(Object fee)  this.Fee = cost; 
    personal Object key;
    personal Object price;

Question: 7. What Is The Following Method Converted To After Type Erasure?
Public Static >
Int Findfirstgreaterthan(t[] At, T Elem) 
// …

Answer:

public static int findFirstGreaterThan(Comparable[] at, Comparable elem) 
    // …
    

J2EE Tutorial Core Java Interview Questions
Question: 8. Will The Following Method Compile? If Not, Why?
Public Static Void Print(listing List) 
For (number N : List)
System.Out.Print(n + ” “);
System.Out.Println();

Answer:

Yes. 

Question: nine. Write A Generic Method To Find The Maximal Element In The Range [start, End) Of A List.

Answer:

import java.Util.*;
public very last magnificence Algorithm 
    public static >
        T max(List list, int begin, int stop) 
       T maxElem = listing.Get(begin);
        for (++begin; begin < end; ++begin)
            if (maxElem.CompareTo(listing.Get(begin)) < 0)
                maxElem = list.Get(begin);
        go back maxElem;
    

JSP Interview Questions
Question: 10. Will The Following Class Compile? If Not, Why?
Public Class Singleton 

Public Static T Getinstance() 
If (example == Null)
Instance = New Singleton();

Return Instance;

Private Static T Instance = Null;

Answer:

No. You can not create a static field of the kind parameter T. 

Core Java Tutorial
Question: 11. Given The Following Classes:
elegance Shape  /* … */ 
magnificence Circle Extends Shape  /* … */ 
magnificence Rectangle Extends Shape  /* … */ 
class Node  /* … */ 
will The Following Code Compile? If Not, Why?
Node Nc = New Node<>();
node Ns = Nc;

Answer:

No. Because Node is not a subtype of Node. 

Java-Springs Interview Questions
Question: 12. Consider This Class:
elegance Node Implements Comparable 
Public Int Compareto(t Obj)  /* … */ 
// …

Will The Following Code Compile? If Not, Why?

Answer:

Yes.

Node node = new Node<>();
Comparable comp = node;

Adv Java Interview Questions
Question: thirteen. What Is A Parameterized Or Generic Type?

Answer:

A regularly occurring type is a kind with formal type parameters. A parameterized kind is an instantiation of a universal kind with real type arguments.

A widespread kind is a reference type that has one or more kind parameters. These type parameters are later replaced via kind arguments whilst the established type is instantiated (or declared ). 

Example (of a regularly occurring type): 
interface Collection    
  public void add (E x);  
  public Iterator iterator(); 

The interface Collection has one kind parameter E .  The type parameter E is an area holder as a way to later get replaced through a kind argument when the widely wide-spread kind is instantiated and used. The instantiation of a normal kind with actual kind arguments is known as a parameterized kind 

Example (of a parameterized kind): 

Collection coll = new LinkedList();

The assertion Collection denotes a parameterized type, which is an instantiation of the normal type Collection ,  where the vicinity holder E has been replaced via the concrete type String .

JSP Tutorial
Question: 14. Can You Give An Example Of A Generic Method?

Answer:

A ordinary type may be declared as a part of technique announcement as well. Then the commonplace kind may be used everywhere within the technique (go back type, parameter type, nearby or block variable kind).

Consider the method under:

    static X doSomething(X wide variety)
        X result = range;
        //do some thing with end result
        go back result;
    
The method can now be called with any Class type expand Number.

Integer i = 5;
Integer okay = doSomething(i);

Question: 15. How Can We Restrict Generics To A Super Class Of Particular Class?

Answer:

In MyListGeneric, Type T is defined as part of class declaration. Any Java Type may be used a kind for this class. If we would need to limit the kinds allowed for a Generic Type, we will use a Generic Restrictions. In statement of the elegance, we special a constraint “T superb Number”. We can use the elegance MyListRestricted with any magnificence that may be a first rate elegance of Number elegance.

JMS(Java Message Service) Interview Questions
Question: 16. How Can We Restrict Generics To A Subclass Of Particular Class?

Answer:

In MyListGeneric, Type T is defined as a part of elegance assertion. Any Java Type may be used a kind for this magnificence. If we’d want to restrict the kinds allowed for a Generic Type, we will use a Generic Restrictions. Consider the instance magnificence underneath: In announcement of the class, we unique a constraint “T extends Number”. We can use the class MyListRestricted with any magnificence extending (any sub magnificence of) Number – Float, Integer, Double and so on.

Magnificence MyListRestricted 
    private List values;
    void upload(T cost) 
        values.Upload(price);
    
    void put off(T fee) 
        values.Do away with(fee);
    
    T get(int index) 
        go back values.Get(index);
    

MyListRestricted restrictedListInteger = new MyListRestricted();
restrictedListInteger.Upload(1);
restrictedListInteger.Upload(2);
String now not valid substitute for constraint “T extends Number”.
//MyListRestricted restrictedStringList = 
//                new MyListRestricted();//COMPILER ERROR

Java-Springs Tutorial
Question: 17. How Do You Declare A Generic Class?

Answer:

Note the assertion of sophistication:Instead of T, We can use any valid identifier.

Magnificence MyListGeneric
Java applet Interview Questions
Question: 18. Can We Use Generics With Array?

Answer:

If you know the truth that Array doesn’t help Generics and that’s why Joshua bloach cautioned to prefer List over Array because List can provide collect time type-safety over Array.

J2EE Interview Questions
Question: 19. Can You Pass List To A Method Which Accepts List