Constraints Imposed Here
We cannot derive a subclass from wrapper classes because it is declared as final. So, the constant functionality of this class never be changed or modified.
Super Classes
byte, short, int, float and double - number class[abstract class]
Boolean and Character – Object
Package
The wrapper classes are part of the java.lang package, which is imported by default into all Java programs.
Sample
int x = 20; - It declares an int variable named x and initializes it with the value 25
Integer y = new Integer(33); - Instantiates an Integer object. The object is initialized with the value 33 and a reference to the object is assigned to the object variable y.
Sample Program
public class WrapperMain {
public static void main(String[] args) {
byte regno = 38;
int totalMark = 416;
float examFees = 3000.50f;
double annualFees = 80000.50d;
// data types to objects - wrapping
Byte regnoObj = new Byte(regno);
Integer totalMarkObj = new Integer(totalMark);
Float examFeesObj = new Float(examFees);
Double annualFeesObj = new Double(annualFees);
System.out.println("Values of Wrapper objects (printing as objects)");
System.out.println("Byte object: " + regnoObj);
System.out.println("Integer object: " + totalMarkObj);
System.out.println("Float object: " + examFeesObj);
System.out.println("Double object: " + annualFeesObj);
// objects to data types - unwrapping
byte byteValue = regnoObj.byteValue();
int integerValue = totalMarkObj.intValue();
float floatValue = examFeesObj.floatValue();
double doubleValue = annualFeesObj.doubleValue();
System.out.println("Unwrapped values (printing as data types)");
System.out.println("byte value: " + byteValue);
System.out.println("int value: " + integerValue);
System.out.println("float value: " + floatValue);
System.out.println("double value: " + doubleValue);
}
}
Mostly Used Methods
parseInt(s) - returns a signed decimal integer value equivalent to string s
toString(i) - returns a new String object representing the integer i
byteValue() - returns the value of this Integer as a byte
doubleValue() - returns the value of this Integer as an double
floatValue() - returns the value of this Integer as a float
intValue() - returns the value of this Integer as an int
longValue() - returns the value of this Integer as a long
shortValue() - returns the value of this Integer as a short
toString() - returns a String object representing the value of this Integer
Usage
It provides various utility functions for primitive types. Like primitive to String, String to binary or hexadecimal etc.
Most of the collection classes store objects and not primitive data types.
