Question

QUESTION 2: Elementary Java Programming (a) Explain what a Wrapper class is in Java and provide an example of one and what it [06] "wraps". (b) You have been given an array of elements to search through for a particular value. [02] Which loop would you choose between a for loop and a for-each loop and why? (c) In Java what is the difference between a StringBuilder and StringBuffer? What [02] are they used for? Total: 10

Answer 1

(a)

A Wrapper class is a class whose object wraps or contains a primitive data types. When we create an object to a wrapper class, it contains a field and in this field, we can store a primitive data types. In other words, we can wrap a primitive value into a wrapper class object.

Need of Wrapper Classes

1. They convert primitive data types into objects. Objects are needed if we wish to modify the arguments passed into a method (because primitive types are passed by value).
2. The classes in java.util package handles only objects and hence wrapper classes help in this case also.
3. Data structures in the Collection framework, such as ArrayList and Vector, store only objects (reference types) and not primitive types.
4. An object is needed to support synchronization in multithreading.

// Java program to demonstrate Wrapping and UnWrapping

// in Java Classes

class WrappingUnwrapping

{

    public static void main(String args[])

    {

        // byte data type

        byte a = 1;

        // wrapping around Byte object

        Byte byteobj = new Byte(a);

        // int data type

        int b = 10;

        //wrapping around Integer object

        Integer intobj = new Integer(b);

        // float data type

        float c = 18.6f;

        // wrapping around Float object

        Float floatobj = new Float(c);

        // double data type

        double d = 250.5;

        // Wrapping around Double object

        Double doubleobj = new Double(d);

        // char data type

        char e='a';

        // wrapping around Character object

        Character charobj=e;

        // printing the values from objects

        System.out.println("Values of Wrapper objects (printing as objects)");

        System.out.println("Byte object byteobj: " + byteobj);

        System.out.println("Integer object intobj: " + intobj);

        System.out.println("Float object floatobj: " + floatobj);

        System.out.println("Double object doubleobj: " + doubleobj);

        System.out.println("Character object charobj: " + charobj);

        // objects to data types (retrieving data types from objects)

        // unwrapping objects to primitive data types

        byte bv = byteobj;

        int iv = intobj;

        float fv = floatobj;

        double dv = doubleobj;

        char cv = charobj;

        // printing the values from data types

        System.out.println("Unwrapped values (printing as data types)");

        System.out.println("byte value, bv: " + bv);

        System.out.println("int value, iv: " + iv);

        System.out.println("float value, fv: " + fv);

        System.out.println("double value, dv: " + dv);

        System.out.println("char value, cv: " + cv);

    }

}

(b)For loop will be used as there are many limitations of for each loop due to which it doesnt fit everywhere.

Limitations of for-each loop

1. For-each loops are not appropriate when you want to modify the array
2. For-each loops do not keep track of index. So we can not obtain array index using For-Each loop
3. For-each only iterates forward over the array in single steps
4. For-each cannot process two decision making statements at once

(c)

Difference between StringBuffer and StringBuilder Java provides three classes to represent a sequence of characters: String, StringBuffer, and StringBuilder. The String class is an immutable class whereas StringBuffer and StringBuilder classes are mutable. There are many differences between StringBuffer and StringBuilder. The StringBuilder class is introduced since JDK 1.5. A list of differences between StringBuffer and StringBuilder are given below: No. StringBuffer StringBuilder 1) StringBuffer is synchronized i.e. thread safe. It means two threads can't call the methods of StringBuffer simultaneously. StringBuilder is non-synchronized i.e. not thread safe. It means two threads can call the methods of StringBuilder simultaneously. 2) StringBuffer is less efficient than StringBuilder. StringBuilder is more efficient than StringBuffer.

The StringBuffer and StringBuilder classes are used when there is a necessity to make a lot of modifications to Strings of characters. Unlike Strings, objects of type StringBuffer and String builder can be modified over and over again without leaving behind a lot of new unused objects.

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