src/java.base/share/classes/java/lang/Number.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
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 * accompanied this code).
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package java.lang;

/**
 * The abstract class {@code Number} is the superclass of platform
 * classes representing numeric values that are convertible to the
 * primitive types {@code byte}, {@code double}, {@code float}, {@code
 * int}, {@code long}, and {@code short}.
 *
 * The specific semantics of the conversion from the numeric value of
 * a particular {@code Number} implementation to a given primitive
 * type is defined by the {@code Number} implementation in question.
 *
 * For platform classes, the conversion is often analogous to a
 * narrowing primitive conversion or a widening primitive conversion
 * as defined in <cite>The Java Language Specification</cite>
 * for converting between primitive types.  Therefore, conversions may
 * lose information about the overall magnitude of a numeric value, may
 * lose precision, and may even return a result of a different sign
 * than the input.
 *
 * See the documentation of a given {@code Number} implementation for
 * conversion details.
 *
 * @author      Lee Boynton
 * @author      Arthur van Hoff
 * @jls 5.1.2 Widening Primitive Conversion
 * @jls 5.1.3 Narrowing Primitive Conversion
 * @since   1.0
 */
public abstract class Number implements java.io.Serializable {
    /**
     * Constructor for subclasses to call.
     */
    public Number() {super();}

    /**
     * Returns the value of the specified number as an {@code int}.
     *
     * @return  the numeric value represented by this object after conversion
     *          to type {@code int}.
     */
    public abstract int intValue();

    /**
     * Returns the value of the specified number as a {@code long}.
     *
     * @return  the numeric value represented by this object after conversion
     *          to type {@code long}.
     */
    public abstract long longValue();

    /**
     * Returns the value of the specified number as a {@code float}.
     *
     * @return  the numeric value represented by this object after conversion
     *          to type {@code float}.
     */
    public abstract float floatValue();

    /**
     * Returns the value of the specified number as a {@code double}.
     *
     * @return  the numeric value represented by this object after conversion
     *          to type {@code double}.
     */
    public abstract double doubleValue();

    /**
     * Returns the value of the specified number as a {@code byte}.
     *
     * @implSpec
     * The default implementation returns the result of {@link #intValue} cast
     * to a {@code byte}.
     *
     * @return  the numeric value represented by this object after conversion
     *          to type {@code byte}.
     * @since   1.1
     */
    public byte byteValue() {
        return (byte)intValue();
    }

    /**
     * Returns the value of the specified number as a {@code short}.
     *
     * @implSpec
     * The default implementation returns the result of {@link #intValue} cast
     * to a {@code short}.
     *
     * @return  the numeric value represented by this object after conversion
     *          to type {@code short}.
     * @since   1.1
     */
    public short shortValue() {
        return (short)intValue();
    }

    /** use serialVersionUID from JDK 1.0.2 for interoperability */
    @java.io.Serial
    private static final long serialVersionUID = -8742448824652078965L;
}