What is difference between == and equals() in java?

== operator is used to compare the references of the objects.

public boolean equals(Object o) is the method provided by the Object class. The default implementation uses ==
operator to compare two objects.

But since the method can be overridden like for String class. equals() method can be used to compare the values of two
objects.

String str1 = new String("MyName"); String str2 = new String("MyName");

if(str1 == str2){
System.out.println(“Objects are equal”)
}else{
System.out.println(“Objects are not equal”)
}

if(str1.equals(str2)){
System.out.println(“Objects are equal”)
}else{
System.out.println(“Objects are not equal”)
}

Output:
Objects are not equal
Objects are equal

Lets look at other snippet:

String str2 = "MyName"; String str3 = str2;

if(str2 == str3){
System.out.println(“Objects are equal”)
}else{
System.out.println(“Objects are not equal”)
}

if(str3.equals(str2)){
System.out.println(“Objects are equal”)
}else{
System.out.println(“Objects are not equal”)
}

Objects are equal
Objects are equal

Can a static block throw exception?

Yes, static block can throw only Runtime exception or can use a try-catch block to catch checked exception.
Typically scenario will be if JDBC connection is created in static block and it fails then exception can be caught, logged and application can exit. If System.exit() is not done, then application may continue and next time if the class is referred JVM will throw NoClassDefFounderror since the class was not loaded by the Classloader.

Quiz #1

What is the o/p of following program ?


public class ForwardRef

{

    int j = getI();

    int i = 5;
    private int getI() { return i; }
    public static void main(String[] args)

    {

        System.out.println(new ForwardRef().j);

    }

}

What is difference between iterator access and index access?

Ans) Index based access allow access of the element directly on the basis of index. The cursor of the datastructure can directly goto the ‘n’ location and get the element. It doesnot traverse through n-1 elements.

In Iterator based access, the cursor has to traverse through each element to get the desired element.So to reach the ‘n’th element it need to traverse through n-1 elements.

Insertion,updation or deletion will be faster for iterator based access if the operations are performed on elements present in between the datastructure.

Insertion,updation or deletion will be faster for index based access if the operations are performed on elements present at last of the datastructure.

Traversal or search in index based datastructure is faster.

ArrayList is index access and LinkedList is iterator access.

Why switch case statement in Java doesnt allow string as input parameter?

Switches based on integers can be optimized to very efficent code. Switches based on other data type can only be compiled to a series of if() statements. For that reason C & C++ only allow switches on integer types, since it was pointless with other types.”

Other opinion is as soon that as you start switching on non-primitives you need to start thinking about “equals” versus “==”.

Firstly comparing two strings can be a fairly lengthy procedure, adding to the performance problems that are mentioned above.

Secondly if there is switching on strings there will be demand for switching on strings ignoring case, switching on strings considering/ignoring locale,switching on strings based on regex