[Chapter 12] Number

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| Chapter 12 The java.lang Package |

# Number

## Name

Number

## Synopsis

Class Name:

  `java.lang.Number`

Superclass:

  `java.lang.Object`

Immediate Subclasses:

  `java.lang.Byte`, `java.lang.Double`,

  `java.lang.Float`, `java.lang.Integer`,

  `java.lang.Long`, `java.lang.Short`,

  `java.math.BigDecimal`,

  `java.math.BigInteger`

Interfaces Implemented:

  `java.io.Serializable`

Availability:

  JDK 1.0 or later

## Description

The `Number` class is an `abstract` class that serves as the superclass for all of the classes that provide object wrappers for primitive numeric values: `byte`, `short`, `int`, `long`, `float`, and `double`. Wrapping a primitive value is useful when you need to treat such a value as an object. For example, there are a number of utility methods that take a reference to an `Object` as one of their arguments. You cannot specify a primitive value for one of these arguments, but you can provide a reference to an object that encapsulates the primitive value. Furthermore, as of JDK 1.1, these wrapper classes are necessary to support the Reflection API and class literals.

The `Number` class defines six methods that must be implemented by its subclasses: `byteValue()`, `shortValue()`, `intValue()`, `longValue()`, `floatValue()`, and `doubleValue()`. This means that a `Number` object can be fetched as an `byte`, `short`, `int`, `long`, `float`, or `double` value, without regard for its actual class.

## Class Summary

    public abstract class java.lang.Number extends java.lang.Number
                                           implements java.io.Serializable {
        // Instance Methods
        public abstract byte byteValue();                  // New in 1.1
        public abstract double doubleValue();
        public abstract float floatValue();
        public abstract int intValue();
        public abstract long longValue();
        public abstract short shortValue();                // New in 1.1
    }

## Instance Methods

### byteValue

#### `public abstract byte byteValue()`

Availability

  New as of JDK 1.1

Returns

  The value of this object as a `byte`.

Description

  This method returns the value of this object as a `byte`. If the data type of the value is not `byte`, rounding may occur.

### doubleValue

#### `public abstract double doubleValue()`

Returns

  The value of this object as a `double`.

Description

  This method returns the value of this object as a `double`. If the data type of the value is not `double`, rounding may occur.

### floatValue

#### `public abstract float floatValue()`

Returns

  The value of this object as a `float`.

Description

  This method returns the value of this object as a `float`. If the data type of the value is not `float`, rounding may occur.

### intValue

#### `public abstract int intValue()`

Returns

  The value of this object as an `int`.

Description

  This method returns the value of this object as an `int`. If the type of value is not an `int`, rounding may occur.

### longValue

#### `public abstract long longValue()`

Returns

  The value of this object as a `long`.

Description

  This method returns the value of this object as a `long`. If the type of value is not a `long`, rounding may occur.

### shortValue

#### `public abstract short shortValue()`

Availability

  New as of JDK 1.1

Returns

  The value of this object as a `short`.

Description

  This method returns the value of this object as a `short`. If the type of value is not a `short`, rounding may occur.

## Inherited Methods

Method | Inherited From | Method | Inherited From
--- | --- | --- | ---
`clone()` | `Object` | `equals(Object)` | `Object`
`finalize()` | `Object` | `getClass()` | `Object`
`hashCode()` | `Object` | `notify()` | `Object`
`notifyAll()` | `Object` | `toString()` | `Object`
`wait()` | `Object` | `wait(long)` | `Object`
`wait(long, int)` | `Object` |  |

## See Also

`Byte`, `Double`, `Float`, `Integer`, `Long`, `Object`, `Short`

NullPointerException |  | NumberFormatException