JSpiders - Wrapper classes
- 2. • Java is not pure object oriented. • Any language which makes use of primitive type of data such languages are not object oriented. • Few purely object oriented languages are Ex: Scala, Smalltalk, Eiffel ..etc • The primitive data types are not objects, they do not belong to any class. • Sometimes, it is required to convert data types into objects in Java language. • A data type can be converted into an object and then used with the help of Wrapper Classes.
- 3. • A wrapper class wraps (encloses) around a data type and gives it an object appearance. • Wherever, the data type is required as an object, Wrapper class object can be used. • Wrapper classes include methods to unwrap the object and give back the data type.
- 4. • It can be compared with a chocolate. The manufacturer wraps the chocolate with some foil or paper to prevent from pollution. The user takes the chocolate, removes and throws the wrapper and eats it.
- 5. To wrap (or to convert) each primitive data type, there comes a wrapper class. Eight wrapper classes exist in java.lang package that represent 8 data types. Following list gives.
- 7. • All wrapper classes are final classes. • All Wrapper classes implements comparable type. • All wrapper classes overrides 3 object class methods 1.toString() 2.hashCode() 3.equals(Object obj)
- 8. Conversion of primitive data to object type is known as Boxing. EX: int k = 100; Integer it1 = new Integer(k); double d = 3.3; Double dt2= new Double(d); Conversion of Object type of data to Primitive type is called as Un-Boxing. EX: int m = it1.intValue(); System.out.println(m); // prints 100 double n = dt2.doubleValue(); System.out.println(n); // prints 3.3
- 9. Boxing and Un-Boxing Can be done implicitly by compiler, it is known as Auto Boxing and Auto Un-Boxing. Integer a1=30; Auto Boxing int l= a1; Auto Un-Boxing
- 10. Wrapper Classes In Collection FrameWorks • Wrapper Classes are used in collection framework. • In Collection we can add only Object type of data. • If primitive data added in Collection Framework then auto boxing and auto un-boxing both happens Implicitly. Ex: ArrayList a1 = new ArrayList(); a1.add(12); a1.add(2356); a1.add(4.5); • Here First auto boxing happens and then up-casting to Object class happens.
- 11. Parsing Technique • Conversion of String type of data to Number format is called as Parsing • For Parsing we make use of parseX() methods which are present in Wrapper classes. Ex: String str = “1234”; int i = Integer.parseInt(str); System.out.println(i); // 1234 • Parsing has to be done carefully, else we may get Exception. • In previous example if String value is “1234g” ,in this case during parsing the value doesn’t match with Integer hence we get NumberFormatException.