Wrapper classes

Java has two categories of data types: primitive and reference. Primitive types are the basic types that store values directly in memory, such as int, char, boolean, and so on. Reference types are the types that store references to objects in memory, such as String, Integer, Boolean, and so on. Objects are instances of classes that have attributes and methods. Reference types are also known as wrapper classes, because they wrap primitive values in objects.

Wrapper class and its associated constructor

Byte => byte and String

Short => short and String

Integer => int and String

Long => long and String

Float => float ,String and double

Double => double and String

Character=> character

Boolean => boolean and String

Wrapper class utiltiy methods

1. valueOf() method

To create a wrapper object from primitive type or String we use valueOf(). It is alternative to constructor of Wrapper class, not suggestable to use. Every Wrapper class, except character class contain static valueOf() to create a Wrapper Object. eg#1.

Integer i=Integer.valueOf("10");

Double d=Double.valueOf("10.5");

Boolean b=Boolean.valueOf("anjan");

System.out.println(i);

System.out.println(d);

System.out.println(b);

2. XXXValue() method

We can use xxxValue() to get primitive type for the given Wrapper Object. These methods are a part of every Number type Object. (Byte,Short,Integer,Long,Float,Double) all these classes have these 6 methods which is Written as shown below.

Methods

public byte byteValue();

public short shortValue();

public int intValue();

public long longValue();

public float floatValue();

public double doubleValue();

eg#1.

Integer i=new Integer(130);

System.out.println(i.byteValue());//-126

System.out.println(i.shortValue());//130

System.out.println(i.intValue());//130

System.out.println(i.longValue());//130

System.out.println(i.floatValue());//130.0

System.out.println(i.doubleValue());//130.0

3. parseXxx() method

We use parseXXXX() to convert String object into primitive type.

form-1

public static primitive parseXXX(String s)

Every wrapper class,except Character class has parseXXX() to convert String into primitive type.

eg:

int i=Integer.parseInt("10");

double d =Double.parseInt("10.5");

boolean b=Boolean.parseBoolean("true");

form-2

public static primitive parseXXXX(String s, int radix) ;

|=> range is from 2 to 36

Every Integral type Wrapper class(Byte,Short,Integer,Long) contains the following parseXXXX() to convert Specified radix String to primitive type.

eg:

int i=Integer.parseInt("1111",2);

System.out.println(i);//15

4. toString() method

To convert the Wrapper Object or primitive to String. Every Wrapper class contain toString().

eg:

String s=Integer.toString(10);

String s=Boolean.toString(true);

String s=Character.toString('a');