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Core Java - Interview Questions and Answers for 'Stringbuffer' - 10 question(s) found - Order By Newest

Very frequently asked in different variations. Frequently asked in Deloitte ( 2 feedback ) , HCL Tech ( 3 feedback ), TCS and Coginizant (CTS)
  Q1. Explain the scenerios to choose between String , StringBuilder and StringBuffer ?

or

What is the difference between String , StringBuilder and StringBuffer ? 		Core Java
Ans. If the Object value will not change, use String Class because a String object is immutable.

If the Object value can change and will only be modified from a single thread, use StringBuilder because StringBuilder is unsynchronized(means faster).

If the Object value may change, and can be modified by multiple threads, use a StringBuffer because StringBuffer is thread safe(synchronized).

  Sample Code for String

  Sample Code for StringBuffer

  Sample Code for StringBuilder

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   Like         Discuss         Correct / Improve     java   string class   string   stringbuilder   stringbuffer   String vs StringBuffer   String vs StringBuilder   String vs StringBuilder vs StringBuffer   StringBuffer vs stringBuilder     Asked in 29 Companies      basic        frequent
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Very frequently asked in HCL Tech ( Based of 4 inputs )
  Q2. Write a Program to reverse a string iteratively and recursivelyCore Java
Ans. Using String method -

new StringBuffer(str).reverse().toString();

Iterative -

Strategy - Loop through each character of a String from last to first and append the character to StringBuilder / StringBuffer

public static String getReverseString(String str){
StringBuffer strBuffer = new StringBuffer(str.length);
for(int counter=str.length -1 ; counter>=0;counter--){
strBuffer.append(str.charAt(counter));
}
return strBuffer;
}

Recursive -

Strategy - Call the method with substring starting from 2nd character recursively till we have just 1 character.

public static String getReverseString(String str){
if(str.length <= 1){
return str;
}
return (getReverseString(str.subString(1)) + str.charAt(0);
}

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   Like         Discuss         Correct / Improve     string  StringBuffer  recursion  for loop  control statements  loop statement  stringbuffer.append  java.lang.String  java.lang.StringBuffer  String Manipulation     Asked in 8 Companies        frequent

 Q3. Which String class does not override the equals() and hashCode() methods, inheriting them directly from class Object?Core Java
Ans. java.lang.StringBuffer.

  Sample Code for StringBuffer

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   Like         Discuss         Correct / Improve     java   object class   stringbuffer      expert        rare

Very frequently asked. Usually asked in different variants like Diff between StringBuffer , String Builder ; Difference between StringBuilder and String class; Choice between these classes etc.
  Q4. What is the difference between StringBuffer and String class ?Core Java
Ans. A string buffer implements a mutable sequence of characters. A string buffer is like a String, but can be modified. At any point in time it contains some particular sequence of characters, but the length and content of the sequence can be changed through certain method calls.

The String class represents character strings. All string literals in Java programs, such as "abc" are constant and implemented as instances of this class; their values cannot be changed after they are created.

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   Like         Discuss         Correct / Improve     java   string   stringbuffer   frequently asked     Asked in 18 Companies      basic        frequent
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Very frequently asked. Usually difference between String,StringBuffer and StringBuilder is asked in different variations.
  Q5. Difference between StringBuffer and StringBuilder ?Core Java
Ans. StringBuffer is synchronized whereas StringBuilder is not.

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   Like         Discuss         Correct / Improve     java   string   stringbuffer   string class   stringbuilder   synchronized   basic interview question   infosys technologies     Asked in 17 Companies      basic        frequent
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Very frequently asked in HCL Tech ( Based of 4 inputs )
  Q6. Write a program to reverse a string iteratively and recursively ?Core Java
Ans. Using String method -

new StringBuffer(str).reverse().toString();

Iterative -

public static String getReverseString(String str){
StringBuffer strBuffer = new StringBuffer(str.length);
for(int counter=str.length -1 ; counter>=0;counter--){
strBuffer.append(str.charAt(counter));
}
return strBuffer;
}

Recursive -

public static String getReverseString(String str){
if(str.length <= 1){
return str;
}
return (getReverseString(str.subString(1)) + str.charAt(0);
}

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   Like         Discuss         Correct / Improve     java   string   reverse   stringbuffer   string class   code     Asked in 6 Companies        frequent

 Q7. what will be the output of this code ?

public static void main(String[] args){
   StringBuffer s1=new StringBuffer("Buggy");                       
   test(s1);                    
   System.out.println(s1);              
}       

private static void test(StringBuffer s){      
   s.append("Bread");   
}		Core Java
Ans.  BuggyBread

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   Like         Discuss         Correct / Improve     java   code   coding   stringbuffer   string   method calling   pass by reference

 Q8. what will be the output of this code ?

public static void main(String[] args)    {          
   String s1=new String("Buggy");                         
   test(s1);                    
   System.out.println(s1);              
}       

private static void test(StringBuffer s){      
   s.append("Bread");   
}		Core Java
Ans.  Buggy

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 Q9. what will be the output of this code ?

public static void main(String[] args)    {          
   StringBuffer s1=new StringBuffer("Buggy");                         
   test(s1);                    
   System.out.println(s1);              
}       

private static void test(StringBuffer s){      
   s=new StringBuffer("Bread");   
}		Core Java
Ans.  Buggy

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 Q10. Can StringBuffer and StringBuilder in Java be inherited?Core Java
Ans. No, they have been declared final and hence cannot be extended.

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   Like         Discuss         Correct / Improve     StringBuffer  StringBuilder

 Q11. Which of the following class creates immutable objects ?Core Java
a. String
b. StringBuffer
c. StringBuilder
d. None of these create immutable objects.

Ans.a. String
 Q12. Which of the following class is synchronized ?Core Java
a. String
b. StringBuffer
c. StringBuilder
d. None of these

Ans.b. StringBuffer
 Q13. Which of the following class cannot be extended or inherited ?

StringBuffer , StringBuilder		Core Java
a. StringBuffer
b. StringBuilder
c. Both cannot be extended
d. Both can be extended

Ans.c. Both cannot be extended

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