Object-Oriented Programming (Narva College) 2017/18 spring

Session 4

Wrapper class

In Java, there are eight primitive data types: byte, short, integer, long, float, double, char and boolean. Unfortunately, not all methods want to operate on primitive data types, but want to get objects as an argument. Hence, we need to convert a primitive data type into an object.

Each of Java's eight primitive data types has a class dedicated to it. These are known as wrapper classes because they wrap the primitive data type into an object of that class.

Each wrapper class has two constructors: one requires String as an argument and the other constructor requires the value of the corresponding data types as an argument. Each of these classes has the following methods:

• doubleValue (returns the value a double)
• floatValue (returns the value a float)
• intValue (returns the value an integer)
• longValue (returns the value a long)
• shortValue (returns the value a short)
• byteValue (returns the value a byte).

The wrapper classes which operate on numbers also have constants MAX_VALUE and MIN_VALUE which hold the values of the minimum and maximum of the corresponding type. See examples:

 System.out.println(Double.MIN_VALUE);
 System.out.println(Byte.MAX_VALUE);
 System.out.println(Integer.MAX_VALUE);

Also these wrapper classes have a static method valueOf which creates a new instance from the Strings:

 Integer intObject = Integer.valueOf("19");

It is also possible to create a value of primitive data type from String using the corresponding parsing methods:

 double arvdouble4 = Double.parseDouble("21");

Session 4