Questions on Library classes

1. Diff between primitive and composite data type

Ans.

2. What is the difference between Integer and int?

Ans.

3. What are wrapper classes and in which library are they included?

Ans.

• A Wrapper class is a class whose object wraps or contains a primitive data types.
• They convert primitive data types into objects. The classes in java.util package handles only objects and hence wrapper classes help

4. What is Autoboxing and Unboxing in Java?

Ans.

Autoboxing: It converts eight primitive data types (short, int, long, float, double, char, byte and boolean) into its corresponding wrapper class object.

Unboxing : It converts wrapper class object into its corresponding primitive data type. It unboxing is reverse of autoboxing.

Example:

public class simply {
     void AutoBoxing_Unboxing(){
          int num= 75;
          Integer n = num;
          System.out.println("After Autoboxing");
          System.out.println("value of wrapper class Integer object n= "+n);
          num=n;
          System.out.println("After Unboxing");
          System.out.println("value of primitive data type int num= "+num);
     }
}

5. What is unboxing? Give an suitable example.

Ans. Unboxing: When we try to assign the object of a wrapper class to primitive type variable it automatically converts the object back to the primitive type, it is called unboxing and it also happens at the time of execution(runtime).

Example:

public class TestWrapper{
    public static void main(String args[]){
        Integer auto =new Integer(500);
        int k= auto;
       System.out.println ( " the value of auto is “+k);
   }
}

6. State the difference between Integer.parseInt() and function Integer.valueOf () Give one example of each.

Ans.

7. What is the difference between isUpperCase() and toUpperCase()?

Ans. isUpperCase( ): This character function returns true if its character argument is an uppercase/capital letter, otherwise it returns false. It returns a boolean result.

toUpperCase( ): This string function converts all the characters of a string in uppercase or capitals.

8. Difference between equals() and compareTo() method. Give one example of each.

Ans.

9. Differentiate between Character.toLowerCase() and Character.isDigit() methods. With an example.

Ans.

10. State the purpose and return data type of the following String functions:

1. indexOf ( )
2. compareTo ( )

Ans.

1. indexOf() returns the index of the character or String passed as the parameter in the string on which is invoked. Return type is int.
2. compareTo() lexicographically compares the String passed as an argument to the String on which it is invoked. Return type is int.

11. Write the difference between length and length() functions.

Ans. length is a property of an array which gives the size of the array. length() is a function of the String class which returns the size of the String.