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Long wrapper class is used to create an object version of a primitive long value.

Constructor of Long wrapper class.




Constructor	Description
Long(long i)	Constructor of Long wrapper class takes a primitive long value.
Long(String str)	Constructor of Long wrapper class also takes a String equivalent of a primitive long value.








Creating the Long wrapper class object.




class A
{
public static void main(String... ar)
{
Long b1 = new Long(10); 	//Boxing primitive long to a Long object.
Long b2 = new Long("20"); 	//Passing primitive long as a String
}
}








Reading the Long wrapper class object.

There are two ways to read a Long object-
• By directly printing the Long object.
• Calling method, longValue() of Long wrapper class, which returns the primitive long equivalent.

class A
{
public static void main(String... ar)
{
Long b1 = new Long(10);		 //Boxing primitive long in a wrapper Long object.
Long b2 = new Long("20"); 	 //Passing primitive long as a String to be boxed in a Long object.


//Unboxing a wrapper Long object.
System.out.println(b1);		 

//Unboxing an Integer object using longValue() method
System.out.println(b2.longValue());

}
}

Output-

10
20

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Some important methods of Long wrapper class

Using compareTo() method to compare values in two Long objects.

Method compareTo(Long l) takes Long class object and it -

• Returns a zero if the invoked Long object contains the value same as l.
• Returns 1 if the invoked Long object contains value larger than l.
• Returns -1 if the invoked Long object contains value smaller than l.

class A
{
public static void main(String... ar)
{ 
Long l1 = new Long("10"); //Constructor accepting String value
Long l2 = new Long(10);	  //Constructor accepting primitive int value

System.out.println("Value in l1 = "+ l1);
System.out.println("Value in l2 = "+ l2);

System.out.println("Invoking l1 to compare with l2 : "+ l1.compareTo(l2));

Long l3 = new Long("15");
Long l4 = new Long(20);

System.out.println("Value in l3 = "+l3);
System.out.println("Value in l4 = "+l4);

System.out.println("Invoking l3 to compare with l4 : "+ l3.compareTo(l4));

System.out.println("Invoking l4 to compare with l3 : "+ l4.compareTo(l3));

}
}

Output-

Value in l1 = 10
Value in l2 = 10
Invoking l1 to compare with l2 : 0
Value in l3 = 15
Value in l4 = 20
Invoking l3 to compare with l4 : -1
Invoking l4 to compare with l3 : 1

Convering a String to a primitive long value, using parseLong() method.

Method parseLong(String s), takes a string and parse it to a primitive long value.

//Converting String to primitive long value.

import java.util.*;

class A
{
public static void main(String... ar)
{
long l1 = Long.parseLong("200");
long l2 = Long.parseLong("-200");

System.out.println("Primitive long value in l1 : "+ l1);
System.out.println("Primitive long value in l2 : "+ l2);
}
}

Output-

Primitive long value in l1 : 200
Primitive long value in l2 : -200

Exception while converting a String to an Long object or a primitive long value

Exception could be caused in two cases -



• When we pass a String value to the constructor of Long class or its method parseInteger(), which cannot be converted to a a primitive long, .
• When we pass an out-of-range value in the form of a String to constructor of Long class or to its parseLong() method, we get a NumberFormatException.


• Exception when converting String to Long object by calling constructor of Long class.

class A
{
public static void main(String... ar)
{
//long l= 100L; works but,
Long b1 = new Long("100L"); //Passing a String value that cannot be converted to a int value.
}
}





Output -




Exception in thread "main" java.lang.NumberFormatException: For input string: "100L"
        at java.lang.NumberFormatException.forInputString(Unknown Source)
        at java.lang.Long.parseLong(Unknown Source)
        at java.lang.Long.(Unknown Source)
        at A.main(Long4.java:8)





• Exception when converting String to primitive long by calling parseLong() method.

class A
{
public static void main(String... ar)
{
int i = Integer.parseInt("-100l"); //Passing a String value that can't be converted to an int.
}
}





Output -




Exception in thread "main" java.lang.NumberFormatException: For input string: "-100L"
        at java.lang.NumberFormatException.forInputString(Unknown Source)
        at java.lang.Long.parseLong(Unknown Source)
        at java.lang.Long.(Unknown Source)
        at A.main(Long4.java:7)








Converting the value stored in a Byte object to all numeric primitive types.




import java.util.*;

class A
{
public static void main(String... ar)
{
Long l = new Long(10000);	//Passing a primitive long value to constructor of wrapper class, Long.

System.out.println("Value in wrapped Long object, l : "+ l);

byte b = l.byteValue();		//Returns a primitive byte value out of a wrapped Long object
short s= l.shortValue();	//Returns a primitive short value out of a wrapped Long object
int i = l.intValue();		//Returns a primitive int value out of a wrapped Long object
long l = l.longValue();		//Returns a primitive long value out of a wrapped Long object
float f = l.floatValue();	//Returns a primitive float value out of a wrapped Long object
double d = l.doubleValue();	//Returns a primitive double value out of a wrapped Long object

System.out.println("byte value of Long object, l : " + b);
System.out.println("short value of Long object, l : " + s);
System.out.println("int value of Long object, l : " + i);
System.out.println("long value of Long object, l : " + l);
System.out.println("float value of Long object, l : " + f);
System.out.println("double value of Long object, l : "+ d);

}
}





Output-




Value in wrapped Long object, l : 10000
byte value of Long object, l : 10000
short value of Long object, l : 10000
int value of Long object, l : 10000
long value of Long object, l : 10000
float value of Long object, l : 10000.0
double value of Long object, l : 10000.0







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