Wrapper Classes

There is a wrapper class for every primitive data type in Java. For example, there’s Integer for int, Character for char, Float for float, Double for double and so on. That is, the class names are same as the data types’ name (Except char and int) apart from the fact that the class names begin with uppercase letters, which is a convention in Java.
We can create objects of these wrapper classes instead of variables of primitive data types.
- Boolean
- Byte
- Short
- Integer
- Long
- Float
- Double
Wrapper classes contains one variable (data member) of their respective primitive data type. They also contain certain functions to manipulate these values.
Why?
- Java — primitive data types ⇒ Not objects ⇒ Wrapper classes
- Also, to make methods available to operate on primitive data types.
All wrapper classes are Immutable Classes
All wrapper classes implement Comparable.

Useful Methods

Syntax

WrapperClass reference_variable = WrapperClass.valueOf(“Number in string format”, base-decimal by default);

Example

Integer i1=Integer.valueOf(“123”);
Integer i2=Integer.valueOf(“101011”,2);
Double d1=Double.valueOf(“3.14”);

Static Method
Xxx can be replaced with any primitive data type
Similar to valueOf() but returns reference to xxx type rather than a wrapper class object.

Syntax

xxx**.**varname = WrapperClass**.**parseXxx(“Number in string format”);

Example

int a=Integer.parseInt(“123”);
double b=Double.parseDouble(“13.45”);

Instance method
Xxx can be replaced with any primitive data type
Returns corresponding primitive data type.
Used to convert from/get the value of a wrapper class object to a primitive data type.
Syntax
```
xxx varname=objectname.xxxValue();
```

Example

//i1 contains a reference of object of Integer class.
int c = i1.intValue();

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Useful Methods