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Java String Classes

Here are 10 essential multiple-choice questions on Java String Classes, covering key concepts.

Last Updated : Mar 27, 2025

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Question 1

Which of the following is immutable in Java?

A
String
B
StringBuffer
C
StringBuilder
D
Both B and C

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Question 2

What is the key difference between StringBuffer and StringBuilder?

A
StringBuffer is thread-safe, StringBuilder is not
B
StringBuilder is synchronized, StringBuffer is not
C
StringBuffer is immutable, StringBuilder is mutable
D
StringBuilder consumes more memory than StringBuffer

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Question 3

Which of the following will compile successfully?

Java

StringBuffer sb = "Hello";

A
No, it will not compile
B
Yes, it will compile
C
Yes, but with a warning
D
Only if sb is declared as final

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Question 4

Which class should be used when multiple threads need to modify the same string?

A
String
B
StringBuffer
C
StringBuilder
D
None of the above

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Question 5

What will be the output of the following code?

Java

String s1 = "Java";
String s2 = s1.concat(" Programming");
System.out.println(s1);

A
Java
B
Java Programming
C
Compilation Error
D
Runtime Exception

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Question 6

Which of the following methods exists in StringBuffer but not in String?

A
append()
B
concat()
C
charAt()
D
length()

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Question 7

What will be the output of the following code?

Java

StringBuilder sb = new StringBuilder("Hello");
sb.append(" World");
System.out.println(sb);

A
Hello
B
Hello World
C
World
D
Compilation Error

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Question 8

Which is the fastest for string modifications in a single-threaded environment?

A
String
B
StringBuffer
C
StringBuilder
D
All are equally fast

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Question 9

What happens if multiple threads try to modify a StringBuilder instance?

A
It will throw a ConcurrentModificationException
B
It may cause unexpected results due to lack of synchronization
C
It will execute sequentially
D
It will behave the same as StringBuffer

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Question 10

What will be the output of the following code?

Java

StringBuffer sb1 = new StringBuffer("Java");
StringBuffer sb2 = sb1;
sb1.append(" Programming");
System.out.println(sb2);

A
Java
B
Java Programming
C
Compilation Error
D
Runtime Exception

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Java Quiz

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