Part 1
String interview questions for experienced in java covered in this post:
What is an immutable class?
- Immutable class means the value or content cannot be changed once an object
is created.
- Best example of immutable in java is the String class. The String object
cannot be changed once it is created.
- All wrapper classes are immutable classes. Wrapper classes are Integer,
Float, Double, Boolean, Byte, Short etc.
Why String is immutable?
- String objects are immutable cause string objects are cached in SCP(String
Constant pool).
- Cached String objects are shared between multiple clients.
- If anyone changed the value of the String object then all clients get
affected. That’s why String is immutable in java.
 
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Can we modify the existing String
object? If I tried to change the existing String object then what will
happen?
-
No we cannot modify the existing String class object.
-
If you are trying to modify an existing string object then
internally new object will be created and if you pointing to a newly created
object to reference variable then the old object will be eligible for
garbage collection.
What is the difference between StringBuilder and StringBuffer?
|
|
StringBuilder |
StringBuffer |
|
1. |
StringBuilder is not a thread-safe. |
StringBuffer is a thread-safe. |
|
2. |
The performance of StringBuilder is good as compare to
StringBuffer. |
The performance of StringBuffer is lower as compare to
StringBuilder cause StringBuffer is thread-safe. |
|
3. |
StringBuilder sb = new StringBuilder(“ac”); |
StringBuffer sb = StringBuffer(“ac”); |
What is the use of the intern()
method?
-
Intern() method returns a canonical representation of
String.
-
In simple word, intern() method return String object from
SCP(String Constant Pool).
What is SCP(String Constant
Pool)?
-
String constant pool is a separate place in heap memory where
all the String objects are stored.
-
If you create an object using a new keyword then the object
gets created on heap memory and keep the same string object into string
constant pool.
-
If you create an object without a new keyword then the object
doesn’t create on heap memory that object will be created on string constant
pool.
-
If an object exists then the reference variable pointing to
an existing object instead of creating a new one.
What is the difference between String
s = "abc" and
String s = new String("abc")?
- String s=”abc”: On this line
String object will not create on heap memory. ‘abc’ string will be directly
stored on the string constant pool.
- String s = new String(“abc”):
new String(“abc”): On this line String object will be created on heap memory
and ‘abc’ will be stored in string constant pool.
List out some inbuilt methods of String
class?
-
String of inbuilt method of String class.
1.
length()
2.
substring()
3.
contains()
4.
equals()
5.
concat()
6.
replace()
7.
isEmpty()
8.
intern()
9.
indexOf()
10.
trim()
11.
toUpperCase()
12.
toLowerCase()
What is the use of trim() method in the
String class?
-
Trim() of String class is used to remove the blank spaces of
String.
-
Trim() method removes blank spaces before and after the
String.
-
Trim() method doesn’t remove the blank spaces in between
String.
How to create an immutable class or
What are the steps to create immutable objects?
-
Please refer to the below steps to create an immutable class.
1.
Create a final class so a subclass is not possible.
2.
Make all instance variables final so no one can change the
value.
3.
Do not provide any setter method just provide a getter
method.
-
For your reference, I have created a new immutable
class.
|
package
simplifiedjava.crackedInterview;
public
final
class
ImmutableClassDemo {
private
final
String empCode="E001";
public
String getEmpCode() {
return
empCode;
}
} |
What is the default size of
StringBuffer and StringBuilder?
-
The default size of StringBuffer and StringBuilder is
16.
What will be the size of StringBuffer
or Builder in the following example?
|
package
simplifiedjava.crackedInterview;
public
class
StringBuilderSizeCalculationDemo {
public
static
void
main(String[] args) {
String s
= "abc";
StringBuffer sb
= new
StringBuffer(s);
System.out.println(sb.capacity());
}
}
Output: 19 |
What will happen if I am trying to keep
adding new characters once the StringBuffer or StringBuilder gets
fulled?
-
The default size of StringBuffer and StringBuilder is 16.
- When StringBuilder or StringBuffer object gets full and we are still
inserting new characters that time internally new StringBuilder or
StringBuffer object gets created copy all content of the old object to new
object.
-
Old objects will be eligible for garbage collection.
Can you specify the scenario where you
can implement String, StringBuffer and StringBuilder?
- String: When content is fixed
and never change throughout life then String is a good option.
-
StringBuffer: When content is
not fixed and the requirement is thread-safety then go for StringBuffer.
- StringBuilder: When content is
not fixed and content would be changing multiple times and no need for
thread safety then go for StringBuilder.
- Java interview questions and answers all MNC - Click here
- Basic core java interview questions and answers for freshers - Click here
- Core java interview questions for 3 years experience - Click here
- Core java interview questions and answers for 3-5 years exp - Click here
- Core java interview questions and Answers for 5 - 7 Years exp - Click here
- Basic Java Interview Questions and Answers - Click here
- Java interview questions and answers on oops - Click here
- Java interview questions and answers on Strings - Click here
- Java interview questions on exception handling - Click here
- Interview questions on multithreading in java for experienced - Click here
- Interview questions on serialization in java for experienced - Click here
- Interview questions on inner class in java for experienced - Click here
- Interview questions on Collections in java for experienced - Click here
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Thank you techies for visiting this blog. I hope you enjoyed this blog and got more technical knowledge. I have tried to cover all types of questions and provided examples tested on eclipse as much as I can. Guys, please don’t just mug up the questions and answers. Try to clear your concepts with examples. Try to write a code on eclipse once you read the concepts. It will help you to memorize the concepts for a very long time. Simultaneously you will be prepared for interview programs as well. It will help you to survive in the IT sector for a long time. It may be easy to crack an interview but it's really tough to survive in the IT industry with inadequate knowledge and skills. I have collected all the questions from actual interviews attended by my friends, colleagues, college mate and classmate. I have covered frequently asked questions as well as challenging questions. I have included many programs to understand the concept thoroughly. I will try to explain the concept with the help of a real-time program in eclipse. You can share more questions which are not covered in this blog or post. Always welcome your suggestions and queries. I will definitely try to resolve it. Please comment your queries and new set of questions under the comment sections. I will create a new post for those questions.
My total experience is 10. Initially I had worked on some
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Softwares. Fortunately, TCS and Cybage has given
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