250+ TOP MCQs on StringBuffer Methods and Answers [2024]

Java MCQs on StringBuffer class’s methods of Java Programming Language.

1. Which of these methods of class StringBuffer is used to extract a substring from a String object?
a) substring()
b) Substring()
c) SubString()
d) None of the mentioned

Answer: a
Clarification: None.

2. What will s2 contain after following lines of Java code?

 StringBuffer s1 = "one";
StringBuffer s2 = s1.append("two")

a) one
b) two
c) onetwo
d) twoone

Answer: c
Clarification: Two strings can be concatenated by using append() method.

3. Which of this method of class StringBuffer is used to reverse sequence of characters?
a) reverse()
b) reverseall()
c) Reverse()
d) reverseAll()

Answer: a
Clarification: reverse() method reverses all characters. It returns the reversed object on which it was called.

4. Which of this method of class StringBuffer is used to get the length of the sequence of characters?
a) length()
b) capacity()
c) Length()
d) Capacity()

Answer: a
Clarification: length()- returns the length of String the StringBuffer would create whereas capacity() returns a total number of characters that can be supported before it is grown.

5. Which of the following are incorrect form of StringBuffer class constructor?
a) StringBuffer()
b) StringBuffer(int size)
c) StringBuffer(String str)
d) StringBuffer(int size , String str)

Answer: d
Clarification: None.

6. What will be the output of the following Java code?

```
    class output 
```
```
    {
```

        public static void main(String args[])

```
        { 
```

             StringBuffer c = new StringBuffer("Hello");

             System.out.println(c.length());

```
        }
```
```
    }
```

a) 4
b) 5
c) 6
d) 7

Answer: b
Clarification: length() method is used to obtain length of StringBuffer object, length of “Hello” is 5.
Output:

$ javac output.java
$ java output
5

7. What will be the output of the following Java code?

```
  class output 
```
```
  {  
```

      public static void main(String args[])

```
      {  
```

          StringBuffer sb=new StringBuffer("Hello");

```
          sb.replace(1,3,"Java");  
```
```
          System.out.println(sb);
```
```
      }  
```
```
  }
```

a) Hello java
b) Hellojava
c) HJavalo
d) Hjava

Answer: c
Clarification: The replace() method replaces the given string from the specified beginIndex and endIndex.

$ javac output.java
$ java output
HJavalo

8. What will be the output of the following Java code?

```
    class output 
```
```
    {
```

        public static void main(String args[])

```
        { 
```

           StringBuffer s1 = new StringBuffer("Hello");

```
           s1.setCharAt(1,'x');
```
```
           System.out.println(s1);
```
```
        }
```
```
    }
```

a) xello
b) xxxxx
c) Hxllo
d) Hexlo

Answer: c
Clarification: None.
Output:

$ javac output.java
$ java output
Hxllo

9. What will be the output of the following Java code?

```
    class output 
```
```
    {
```

        public static void main(String args[])

```
        {
```

           StringBuffer s1 = new StringBuffer("Hello World");

```
           s1.insert(6 , "Good ");
```
```
           System.out.println(s1);
```
```
        }
```
```
   }
```

a) HelloGoodWorld
b) HellGoodoWorld
c) HellGood oWorld
d) Hello Good World

Answer: d
Clarification: The insert() method inserts one string into another. It is overloaded to accept values of all simple types, plus String and Objects. Sting is inserted into invoking object at specified position. “Good ” is inserted in “Hello World” T index 6 giving “Hello Good World”.
output:

$ javac output.java
$ java output 
Hello Good World

10. What will be the output of the following Java code?

```
    class output 
```
```
    {
```

        public static void main(String args[])

```
        { 
```

           StringBuffer s1 = new StringBuffer("Hello");

```
           s1.insert(1,"Java");
```
```
           System.out.println(s1);
```
```
        }
```
```
    }
```

a) hello
b) java
c) Hello Java
d) HJavaello

Answer: d
Clarification: Insert method will insert string at a specified position
Output:

$ javac output.java
$ java output
HJavaello

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