Java MCQs on StringBuffer class of Java Programming Language.
1. Which of these class is used to create an object whose character sequence is mutable? Answer: b 2. Which of this method of class StringBuffer is used to concatenate the string representation to the end of invoking string? Answer: b 3. Which of these method of class StringBuffer is used to find the length of current character sequence? Answer: a 4. What is the string contained in s after following lines of Java code? a) Hell Answer: b 5. Which of the following statement is correct? Answer: a 6. What will be the output of the following Java program? a) 6 4 6 9 7. What will be the output of the following Java program? a) He 8. What will be the output of the following Java program? a) Hello 9. What will be the output of the following Java program? a) Hello 10. What will be the output of the following Java program? a) b) c) d)
a) String()
b) StringBuffer()
c) String() & StringBuffer()
d) None of the mentioned
Clarification: StringBuffer represents growable and writable character sequence.
a) concat()
b) append()
c) join()
d) concatenate()
Clarification: None.
a) length()
b) Length()
c) capacity()
d) Capacity()
Clarification: None.StringBuffer s new StringBuffer("Hello");
s.deleteCharAt(0);
b) ello
c) Hel
d) llo
Clarification: deleteCharAt() method deletes the character at the specified index location and returns the resulting StringBuffer object.
a) reverse() method reverses all characters
b) reverseall() method reverses all characters
c) replace() method replaces first occurrence of a character in invoking string with another character
d) replace() method replaces last occurrence of a character in invoking string with another character
Clarification: reverse() method reverses all characters. It returns the reversed object on which it was called.
class output
{
public static void main(String args[])
{
String a = "hello i love java";
System.out.println(a.indexOf('e')+" "+a.indexOf('a')+" "+a.lastIndexOf('l')+" "+a.lastIndexOf('v'));
}
}
b) 5 4 5 9
c) 7 8 8 9
d) 1 14 8 15
Clarification: indexof(‘c’) and lastIndexof(‘c’) are pre defined function which are used to get the index of first and last occurrence of
the character pointed by c in the given array.
Output:
$ javac output.java
$ java output
1 14 8 15
class output
{
public static void main(String args[])
{
StringBuffer c = new StringBuffer("Hello");
c.delete(0,2);
System.out.println(c);
}
}
b) Hel
c) lo
d) llo
Clarification: delete(0,2) is used to delete the characters from 0 th position to 1 st position.
Output:
$ javac output.java
$ java output
llo
class output
{
public static void main(String args[])
{
StringBuffer c = new StringBuffer("Hello");
StringBuffer c1 = new StringBuffer(" World");
c.append(c1);
System.out.println(c);
}
}
b) World
c) Helloworld
d) Hello World
Clarification: append() method of class StringBuffer is used to concatenate the string representation to the end of invoking string.
Output:
$ javac output.java
$ java output
Hello World
class output
{
public static void main(String args[])
{
StringBuffer s1 = new StringBuffer("Hello");
StringBuffer s2 = s1.reverse();
System.out.println(s2);
}
}
b) olleH
c) HelloolleH
d) olleHHello
Clarification: reverse() method reverses all characters. It returns the reversed object on which it was called.
Output:
$ javac output.java
$ java output
olleH
class output
{
class output
{
public static void main(String args[])
{
char c[]={'A', '1', 'b' ,' ' ,'a' , '0'};
for (int i = 0; i < 5; ++i)
{
i++;
if(Character.isDigit(c[i]))
System.out.println(c[i]+" is a digit");
if(Character.isWhitespace(c[i]))
System.out.println(c[i]+" is a Whitespace character");
if(Character.isUpperCase(c[i]))
System.out.println(c[i]+" is an Upper case Letter");
if(Character.isLowerCase(c[i]))
System.out.println(c[i]+" is a lower case Letter");
i++;
}
}
}
a is a lower case Letter
is White space character
b is a lower case Letter
is White space character
1 is a digit
a is a lower case Letter
a is a lower case Letter
0 is a digit
Clarification: Character.isDigit(c[i]), Character.isUpperCase(c[i]), Character.isWhitespace(c[i]) are the function of library java.lang they are used to find whether the given character is of specified type or not. They return true or false i:e Boolean variable.
Output:
$ javac output.java $ java output 1 is a digit a is a lower case Letter