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Introduction to wrapper class in java:

Wrapper Class :

  • Java uses primitive types, such as int, char, double to hold the basic data types supported by the language.
  • Sometimes it is required to create an object representation of these primitive types.
  • These are collection classes that deal only with such objects. One needs to wrap the primitive type in a class.
  • To satisfy this need, java provides classes that correspond to each of the primitive types. Basically, these classes encapsulate, or wrap, the primitive types within a class.
  • Thus, they are commonly referred to as type wrapper. Type wrapper are classes that encapsulate a primitive type within an object.
  • The wrapper types are Byte, Short, Integer, Long, Character, Boolean, Double, Float.

These classes offer a wide array of methods that allow to fully integrate the primitive types into Java’s object hierarchy.

 

Wrapper classes for converting simple types

 

Simple Type

Wrapper class

boolean

Boolean

char

Character

double

Double

float

Float

int

Integer

long

Long

 

Converting primitive numbers to Object numbers using constructor methods

 

Constructor calling

Conversion Action

Integer IntVal = new Integer(i);

Primitive integer to Integer object

Float FloatVal = new Float(f);

Primitive float to Float object

Double DoubleVal = new Double(d);

Primitive double to Double object

Long LongVal = new Long(l);

Primitive long to Long object

 

NOTE : I, f, d and l are primitive data values denoting int, float, double and long data types. They may be constants or variables.

 

Converting Object numbers to Primitive numbers using typeValue() method

 

Method calling

Conversion Action

int i = IntVal.intValue();

Object to primitive integer

float f = FloatVal.floatValue();

Object to primitive float

double d = DoubleVal.doubleValue();

Object to primitive double

long l = LongVal.longValue();

Object to primitive long

 

Converting Numbers to Strings using toString() method

 

Method calling

Conversion Action

str = Integer.toString(i);

Primitive integer i to String str

str = Float.toString(f);

Primitive float f  to String str

str = Double.toString(d);

Primitive double d to String str

str = Long.toString(l);

Primitive long l to String str

 

Converting String Object in to Numeric Object using static method ValueOf()

 

Method calling

Conversion Action

IntVal = Integer.ValueOf(str);

Convert String into Integer object

FloatVal = Float.ValueOf(str);

Convert String into Float object

DoubleVal = Double.ValueOf(str);

Convert String into Double object

LongVal = Long.ValueOf(str);

Convert String into Long object

 

Converting Numeric Strings to Primitive numbers using Parsing method

 

Method calling

Conversion Action

int i = Integer.parseInt(str);

Converts String str into primitive integer i

long l = Long.parseLong(str);

Converts String str into primitive long l

 

NOTE : parseInt() and parseLong() methods throw a NumberFormatException if the value of the str does not represent an integer.