Java.lang.Number Class in Java

Most of the time, while working with numbers in java, we use primitive data types. But, Java also provides various numeric wrapper sub classes under the abstract class Number present in java.lang package. There are mainly six sub-classes under Number class.These sub-classes define some useful methods which are used frequently while dealing with numbers.
 

These classes "wrap" the primitive data type in a corresponding object. Often, the wrapping is done by the compiler. If you use a primitive where an object is expected, the compiler boxes the primitive in its wrapper class for you. Similarly, if you use a Number object when a primitive is expected, the compiler unboxes the object for you. This is also called Autoboxing and Unboxing.
Why to use a Number class object over primitive data? 
 

• Constants defined by the number class, such as MIN_VALUE and MAX_VALUE, that provide the upper and lower bounds of the data type are very much useful.
• Number class object can be used as an argument of a method that expects an object (often used when manipulating collections of numbers).
• Class methods can be used for converting values to and from other primitive types, for converting to and from strings, and for converting between number systems (decimal, octal, hexadecimal, binary).

Methods common to all sub classes of Number: 
 

1. xxx xxxValue() : Here xxx represent primitive number data types (byte, short, int, long, float, double). This method is used to convert the value of this Number object to the primitive data type specified. 
    

Syntax : 
byte byteValue()
short shortValue()
int intValue()
long longValue()
float floatValue()
double doubleValue()
Parameters : 
----
Returns :
the numeric value represented by this object
after conversion to specified type

//Java program to demonstrate xxxValue() method
public class Test
{
    public static void main(String[] args) 
    {
        // Creating a Double Class object with value "6.9685"
        Double d = new Double("6.9685");
    
        // Converting this Double(Number) object to 
        // different primitive data types
        byte b = d.byteValue(); 
        short s = d.shortValue(); 
        int i = d.intValue(); 
        long l = d.longValue(); 
        float f = d.floatValue(); 
        double d1 = d.doubleValue(); 
            
        System.out.println("value of d after converting it to byte : " + b);
        System.out.println("value of d after converting it to short : " + s);
        System.out.println("value of d after converting it to int : " + i);
        System.out.println("value of d after converting it to long : " + l);
        System.out.println("value of d after converting it to float : " + f);
        System.out.println("value of d after converting it to double : " + d1);
    }
}

Output: 
 

value of d after converting it to byte : 6
value of d after converting it to short : 6
value of d after converting it to int : 6
value of d after converting it to long : 6
value of d after converting it to float : 6.9685
value of d after converting it to double : 6.9685

Note : While converting, possible loss of precision may occur. For example, as we can see that fraction part(".9685") has been left out while converting from Double object to int data type. 
 

• int compareTo(NumberSubClass referenceName) : This method is used to compare this Number object to the argument specified. However, two different types cannot be compared, so both the argument and the Number object that invoke the method should be of the same type.The referenceName could be a Byte, Double, Integer, Float, Long, or Short. 
   

Syntax : 
public int compareTo( NumberSubClass referenceName )
Parameters : 
referenceName - any NumberSubClass type value
Returns :
the value 0 if the Number is equal to the argument.
the value 1 if the Number is less than the argument.
the value -1 if the Number is greater than the argument.

//Java program to demonstrate compareTo() method
public class Test
{
    public static void main(String[] args) 
    {
        // creating an Integer Class object with value "10"
        Integer i = new Integer("10");
    
        // comparing value of i
        System.out.println(i.compareTo(7)); 
        System.out.println(i.compareTo(11)); 
        System.out.println(i.compareTo(10)); 
    }
}

Output: 
 

1
-1
0

• boolean equals(Object obj) : This method determine whether this Number object is equal to the argument. 
   

Syntax : 
public boolean equals(Object obj)
Parameters : 
obj - any object
Returns :
The method returns true if the argument is not null and 
is an object of the same type and with the same numeric value,
otherwise false.

//Java program to demonstrate equals() method
public class Test
{
    public static void main(String[] args)
    {
        // creating a Short Class object with value "15"
        Short s = new Short("15");
    
        // creating a Short Class object with value "10"
        Short x = 10;
    
        // creating an Integer Class object with value "15"
        Integer y = 15;
    
        // creating another Short Class object with value "15"
        Short z = 15;
    
        //comparing s with other objects
        System.out.println(s.equals(x));
        System.out.println(s.equals(y));
        System.out.println(s.equals(z));
    }
}

Output: 
 

false
false
true

• int parseInt(String s,int radix) : This method is used to get the primitive data type of a String. Radix is used to return decimal(10), octal(8), or hexadecimal(16) etc representation as output. 
   

Syntax : 
static int parseInt(String s, int radix)
Parameters : 
s - any String representation of decimal
radix - any radix value
Returns :
the integer value represented by the argument in decimal.
Throws :
NumberFormatException : if the string does not contain a parsable integer.

//Java program to demonstrate Integer.parseInt() method
public class Test
{
    public static void main(String[] args)
    {
        // parsing different strings
        int z = Integer.parseInt("654",8); 
        int a = Integer.parseInt("-FF", 16);
        long l = Long.parseLong("2158611234",10); 
            
        System.out.println(z);
        System.out.println(a);
        System.out.println(l);
            
        // run-time NumberFormatException will occur here
        // "Geeks" is not a parsable string
        int x = Integer.parseInt("Geeks",8); 
            
        // run-time NumberFormatException will occur here
        // (for octal(8),allowed digits are [0-7])
        int y = Integer.parseInt("99",8); 
            
    }
}

Output: 
 

428
-255
2158611234
Exception in thread "main" java.lang.NumberFormatException: For input string: "Geeks"
    at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
    at java.lang.Integer.parseInt(Integer.java:580)
    at Test.main(Test.java:17)

• int parseInt(String s) : This method is another variant of above method where by default radix is 10(decimal). 
   

Syntax : 
static int parseInt(String s)
Parameters : 
s - any String representation of decimal
Returns :
the integer value represented by the argument in decimal.
Throws :
NumberFormatException : if the string does not contain a parsable integer.

//Java program to demonstrate Integer.parseInt() method
public class Test
{
    public static void main(String[] args) 
    {
        // parsing different strings
        int z = Integer.parseInt("654"); 
        long l = Long.parseLong("2158611234"); 
            
        System.out.println(z);
        System.out.println(l);
            
        // run-time NumberFormatException will occur here
        // "Geeks" is not a parsable string
        int x = Integer.parseInt("Geeks"); 
            
        // run-time NumberFormatException will occur here
        // (for decimal(10),allowed digits are [0-9])
        int a = Integer.parseInt("-FF");
            
    }
}

Output: 
 

654
2158611234
Exception in thread "main" java.lang.NumberFormatException: For input string: "Geeks"
    at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
    at java.lang.Integer.parseInt(Integer.java:580)
    at java.lang.Integer.parseInt(Integer.java:615)
    at Test.main(Test.java:15)

• String toString() : There are two variants of toString() method. They are used to get String representation of a number. The other variants of these methods are Integer.toBinaryString(int i), Integer.toHexString(int i), Integer.toOctalString(int i) which will return binary, hexa-decimal, octal string representation of specified integer(i) respectively. 
   

Syntax : 
String toString()
String toString(int i)
Parameters : 
String toString() - no parameter
String toString(int i) - i: any integer value
Returns :
String toString() -
returns a String object representing the value of the Number object 
on which it is invoked.
String toString(int i) -
returns a decimal String object representing the specified integer(i)

//Java program to demonstrate Integer.toString() 
//and Integer.toString(int i) method
public class Test
{
    public static void main(String[] args)
    {
        // demonstrating toString() method
        Integer x = 12;
        
        System.out.println(x.toString()); 
        
        // demonstrating toString(int i) method
        System.out.println(Integer.toString(12));
        
        System.out.println(Integer.toBinaryString(152));
        System.out.println(Integer.toHexString(152)); 
        System.out.println(Integer.toOctalString(152));
    }
}

Output: 
 

12
12
10011000
98
230

• Integer valueOf() : There are three variants of valueOf() method. All these three methods return an Integer object holding the value of a primitive integer. 
   

Syntax : 
Integer valueOf(int i)
Integer valueOf(String s)
Integer valueOf(String s, int radix)
Parameters : 
i - any integer value
s - any String representation of decimal
radix - any radix value
Returns :
valueOf(int i) : an Integer object holding the valuerepresented by the int argument.
valueOf(String s) : an Integer object holding value represented by the string argument.
valueOf(String s, int radix) : an Integer object holding the value
 represented by the string argument with base radix.
Throws :
valueOf(String s) -
NumberFormatException : if the string does not contain a parsable integer.
valueOf(String s, int radix) -
NumberFormatException : if the string does not contain a parsable integer.

// Java program to demonstrate valueOf() method
public class Test
{
    public static void main(String[] args)
    {
        // demonstrating valueOf(int i) method
        System.out.println("Demonstrating valueOf(int i) method");
        Integer i =Integer.valueOf(50); 
        Double d = Double.valueOf(9.36); 
        System.out.println(i);
        System.out.println(d);
            
        // demonstrating valueOf(String s) method
        System.out.println("Demonstrating valueOf(String s) method");
        Integer n = Integer.valueOf("333"); 
        Integer m = Integer.valueOf("-255"); 
        System.out.println(n);
        System.out.println(m);
            
        // demonstrating valueOf(String s,int radix) method
        System.out.println("Demonstrating (String s,int radix) method");
        Integer y = Integer.valueOf("333",8); 
        Integer x = Integer.valueOf("-255",16); 
        Long l = Long.valueOf("51688245",16); 
        System.out.println(y);
        System.out.println(x);
        System.out.println(l);
            
        // run-time NumberFormatException will occur in below cases
        Integer a = Integer.valueOf("Geeks");
        Integer b = Integer.valueOf("Geeks",16); 
    }
}

Output: 
 

Demonstrating valueOf(int i) method
50
9.36
Demonstrating valueOf(String s) method
333
-255
Demonstrating (String s,int radix) method
219
-597
1365803589

Exception in thread "main" java.lang.NumberFormatException: For input string: "Geeks"
    at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
    at java.lang.Integer.parseInt(Integer.java:580)
    at java.lang.Integer.valueOf(Integer.java:766)
    at Test.main(Test.java:28)

Practice Question: 
What is the output of the given java code? 
 

public class Test
{
   public static void main(String[] args)
   {
       Integer i = Integer.parseInt("Kona", 27);
       System.out.println(i);
   }
}

Options : 
 

A) NumberFormatException at run-time
B) NumberFormatException at compile-time
C) 411787

Answer : 
 

C) 411787

Explanation : 
Since radix is 27,so allowed characters in a String literal are [0-9],[A-Q](for 10 to 26).So its value will calculated as follows: 
=> a*(27^0) + n*(27^1) + o*(27^2) + k*(27^3) 
=> 10*1 + 23*27 + 24*27*27 + 20*27*27*27 
=> 10 + 621 + 17496 + 393660 
=> 411787