版权
/*
* Copyright (c) 1994, 2013, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
版权所有，甲骨文和/或其附属公司版权所有。
甲骨文专有/机密。使用受许可条款约束。
包和依赖
package java.lang;
import java.lang.annotation.Native;
The Integer class wraps a value of the primitive type int in an object. An object of type Integer contains a single field whose type is int.
In addition, this class provides several methods for converting an int to a String and a String to an int, as well as other constants and methods useful when dealing with an int.
Implementation note: The implementations of the "bit twiddling" methods (such as highestOneBit and numberOfTrailingZeros) are based on material from Henry S. Warren, Jr.'s Hacker's Delight, (Addison Wesley, 2002).
Since:
JDK1.0
Author:
Lee Boynton, Arthur van Hoff, Josh Bloch, Joseph D. Darcy
Integer是在java.lang包下的
导入了Native依赖
Integer类将基本类型int的值包装在对象中。整型对象包含一个整型字段。
此外，该类还提供了几种将int转换为字符串和字符串转换为int的方法，以及处理int时有用的其他常量和方法。
实施说明：“比特旋转”方法（如highestOneBit和numberOfTrailingZeros）的实施基于小亨利·S·沃伦（Henry S.Warren，Jr.）的《黑客之乐》（Addison Wesley，2002）中的材料。
自：
JDK1.0
作者：
李·博因顿、阿瑟·范霍夫、乔希·布洛赫、约瑟夫·D·达西
Native
再来看下导入的Native，它实际上是个接口
/*
* Copyright (c) 2012, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package java.lang.annotation;
/**
* Indicates that a field defining a constant value may be referenced
* from native code.
*
* The annotation may be used as a hint by tools that generate native
* header files to determine whether a header file is required, and
* if so, what declarations it should contain.
*
* @since 1.8
*/
@Documented
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.SOURCE)
public @interface Native {
}
指示可以引用定义常量值的字段
来自本机代码。
生成本机注释的工具可以将注释用作提示
头文件，以确定是否需要头文件，以及
如果是，它应该包含哪些声明。
@从1.8开始
注释
他有三个元注解
@Documented
@Documented： 将注解中的元素包含到Javadoc中
@Target(ElementType.FIELD)
@Target(ElementType.XXX)：说明修饰的成员关系
constructor
描述构造器
Field
描述域
Local_variable
描述局部变量
method
描述方法
package
描述包
type
描述类、接口
@Retention(RetentionPolicy.SOURCE)
@Retention(RetentionPolicy.XXX)：定义了注解被保留的时间长短
source
只在源码阶段保留，编译时被忽视
class
只被保留到编译进行时，不进JVM
Runtime
保留到程序进行时，会进JVM
总结
这个接口的作用就是调用本地方法库里面的用C语言写的方法
继承和实现
public final class Integer extends Number implements Comparable<Integer> {
可以看出，Integer继承了Number类，实现了Comparable接口
Number 类
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 defining 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 Conversions
* @jls 5.1.3 Narrowing Primitive Conversions
* @since JDK1.0
*/
public abstract class Number implements java.io.Serializable {
/**
* Returns the value of the specified number as an {@code int},
* which may involve rounding or truncation.
*
* @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},
* which may involve rounding or truncation.
*
* @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},
* which may involve rounding.
*
* @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},
* which may involve rounding.
*
* @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},
* which may involve rounding or truncation.
*
* <p>This 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 JDK1.1
*/
public byte byteValue() {
return (byte)intValue();
}
/**
* Returns the value of the specified number as a {@code short},
* which may involve rounding or truncation.
*
* <p>This 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 JDK1.1
*/
public short shortValue() {
return (short)intValue();
}
/** use serialVersionUID from JDK 1.0.2 for interoperability */
private static final long serialVersionUID = -8742448824652078965L;
}
抽象类{@code Number}是平台的超类
表示可转换为基本类型byte、double、float、int、long、short
从给定原语的特定Number实现类型由所讨论的Number实现定义。
对于平台类，转换通常类似于缩小原语转换或扩大原语转换
如《爪哇与贸易》中所定义；语言规范
用于在基元类型之间转换。因此，转换可能会发生可能会丢失有关数值整体大小的信息失去精度，甚至可能返回不同符号的结果
而不是输入。
有关详细信息，请参阅给定Number实现的文档
转换细节。
@作者李·博因顿
@作者阿瑟·范霍夫
@jls 5.1.2扩大原语转换
@jls 5.1.3缩小原语转换范围
@从JDK1.0开始
public abstract int intValue();
以整数形式返回指定数字的值，这可能涉及舍入或截断。
返回：转换为int类型后此对象表示的数值。
public abstract long longValue();
以long形式返回指定数字的值，这可能涉及舍入或截断。
返回：转换为long类型后此对象表示的数值。
public abstract float floatValue();
以浮点形式返回指定数字的值，这可能涉及舍入。
返回：转换为float类型后，此对象表示的数值。
public abstract double doubleValue();
以双精度形式返回指定数字的值，这可能涉及舍入。
返回：转换为double类型后此对象表示的数值。
public byte byteValue()
public byte byteValue() {
return (byte)intValue();
}
形式返回指定数字的值，这可能涉及舍入或截断。
此实现将intValue转换的结果返回到一个字节。
返回：此对象在转换为字节类型后表示的数值。
自：JDK1.1.
public short shortValue()
public short shortValue() {
return (short)intValue();
}
以短字符形式返回指定数字的值，这可能涉及舍入或截断。
此实现将intValue cast的结果返回给short。
返回：转换为short类型后此对象表示的数值。
自：JDK1.1.
private static final long serialVersionUID = -8742448824652078965L;
使用JDK 1.0.2中的serialVersionUID实现互操作性
