Java虚拟机规范9：深入解析Java SE 9 JVM

需积分: 9 88 浏览量更新于2024-07-19 收藏 2.2MB PDF 举报

"Java虚拟机规范9是Oracle官方发布的关于Java SE 9版本的JVM规范文档，由Tim Lindholm、Frank Yellin、Gilad Bracha和Alex Buckley等人撰写，于2017年9月发布。该文档详细阐述了Java虚拟机的结构、类文件格式、数据类型等内容，并提供了反馈机制。" Java虚拟机（JVM）是Java程序运行的核心，它负责将编译后的字节码转化为机器语言并执行。在Java SE 9版的JVM规范中，有以下几个主要知识点： 1. **历史背景**：Java虚拟机自Java诞生以来，经历了多次重大更新，每次更新都旨在提高性能、优化内存管理和增强安全性。Java SE 9是这个历程中的一个重要里程碑，引入了模块系统（Project Jigsaw）等新特性。 2. **组织结构**：JVM规范文档通常包括多个部分，如介绍、JVM的结构、类文件格式、操作数栈、运行时数据区、指令集、异常处理、线程和内存管理等。这些部分详细描述了JVM如何解析和执行Java代码。 3. **类文件格式**：Java程序编译后生成的.class文件遵循特定的格式，包括魔数、版本信息、常量池、字段表、方法表等组成部分。这个格式是JVM识别和加载类的基础。 4. **数据类型**：JVM支持两种类型的数据：原始类型（Primitive Types）和引用类型（Reference Types）。原始类型包括整型（如byte、short、int、long）、浮点型（float、double）、字符型（char）和布尔型（boolean）。其中，浮点型值集定义了浮点数的表示方式。 5. **基本类型的值与范围**：对于原始类型，规范详细定义了它们的取值范围和存储大小，例如，int类型占用32位，范围从-2^31到2^31-1；float和double分别代表单精度和双精度浮点数。 6. **返回地址类型**：在JVM中，当方法被调用时，会有一个返回地址保存在堆栈上，用于在方法结束时返回调用者。这个返回地址类型是JVM执行控制流的关键部分。 7. **布尔类型**：boolean类型在JVM中以整型值的形式存在，通常使用1个字节表示，但不直接对应字节码指令，而是通过其他整型指令来实现逻辑运算。 8. **操作数栈与局部变量表**：在执行过程中，JVM使用操作数栈进行计算，局部变量表则存储方法参数和局部变量。这两个组件构成了方法执行的核心数据结构。 9. **内存模型**：JVM内存模型包括堆、栈、方法区、程序计数器和本地方法栈等区域，它们各自承担不同的角色，如堆存储对象实例，栈存储方法调用上下文。 10. **指令集**：JVM有一套二进制指令集，如aload、istore等，这些指令控制着JVM的执行流程。每个指令都有特定的含义和操作，如加载、存储、算术运算、分支、跳转等。《Java虚拟机规范9》详细规定了Java SE 9版JVM的各个方面，是理解和调试Java应用程序的基础，对于开发者来说具有极高的参考价值。通过深入学习这个规范，开发者可以更好地理解Java程序的运行机制，优化代码性能，以及解决运行时问题。

2.2 Data Types THE STRUCTURE OF THE JAVA VIRTUAL MACHINE

2.2 Data Types

Like the Java programming language, the Java Virtual Machine operates on two

kinds of types: primitive types and reference types. There are, correspondingly, two

kinds of values that can be stored in variables, passed as arguments, returned by

methods, and operated upon: primitive values and reference values.

The Java Virtual Machine expects that nearly all type checking is done prior

to run time, typically by a compiler, and does not have to be done by the Java

Virtual Machine itself. Values of primitive types need not be tagged or otherwise

be inspectable to determine their types at run time, or to be distinguished from

values of reference types. Instead, the instruction set of the Java Virtual Machine

distinguishes its operand types using instructions intended to operate on values of

specific types. For instance, iadd, ladd, fadd, and dadd are all Java Virtual Machine

instructions that add two numeric values and produce numeric results, but each is

specialized for its operand type: int, long, float, and double, respectively. For a

summary of type support in the Java Virtual Machine instruction set, see §2.11.1.

The Java Virtual Machine contains explicit support for objects. An object is

either a dynamically allocated class instance or an array. A reference to an object

is considered to have Java Virtual Machine type reference. Values of type

reference can be thought of as pointers to objects. More than one reference to an

object may exist. Objects are always operated on, passed, and tested via values of

type reference.

2.3 Primitive Types and Values

The primitive data types supported by the Java Virtual Machine are the numeric

types, the boolean type (§2.3.4), and the returnAddress type (§2.3.3).

The numeric types consist of the integral types (§2.3.1) and the floating-point types

(§2.3.2).

The integral types are:

• byte, whose values are 8-bit signed two's-complement integers, and whose

default value is zero

• short, whose values are 16-bit signed two's-complement integers, and whose

default value is zero

2.3 Primitive Types and Values THE STRUCTURE OF THE JAVA VIRTUAL MACHINE

2.3.2 Floating-Point Types, Value Sets, and Values

The floating-point types are float and double, which are conceptually associated

with the 32-bit single-precision and 64-bit double-precision format IEEE 754

values and operations as specified in IEEE Standard for Binary Floating-Point

Arithmetic (ANSI/IEEE Std. 754-1985, New York).

The IEEE 754 standard includes not only positive and negative sign-magnitude

numbers, but also positive and negative zeros, positive and negative infinities, and

a special Not-a-Number value (hereafter abbreviated as "NaN"). The NaN value

is used to represent the result of certain invalid operations such as dividing zero

by zero.

Every implementation of the Java Virtual Machine is required to support two

standard sets of floating-point values, called the float value set and the double value

set. In addition, an implementation of the Java Virtual Machine may, at its option,

support either or both of two extended-exponent floating-point value sets, called

the float-extended-exponent value set and the double-extended-exponent value set.

These extended-exponent value sets may, under certain circumstances, be used

instead of the standard value sets to represent the values of type float or double.

The finite nonzero values of any floating-point value set can all be expressed in

the form s ⋅ m ⋅ 2

(e - N + 1)

, where s is +1 or -1, m is a positive integer less than

, and e is an integer between E

min

= -(2

K-1

-2) and E

max

= 2

K-1

-1, inclusive, and

where N and K are parameters that depend on the value set. Some values can

be represented in this form in more than one way; for example, supposing that a

value v in a value set might be represented in this form using certain values for

s, m, and e, then if it happened that m were even and e were less than 2

K-1

, one

could halve m and increase e by 1 to produce a second representation for the same

value v. A representation in this form is called normalized if m ≥ 2

N-1

; otherwise

the representation is said to be denormalized. If a value in a value set cannot be

represented in such a way that m ≥ 2

N-1

, then the value is said to be a denormalized

value, because it has no normalized representation.

The constraints on the parameters N and K (and on the derived parameters E

min

and E

max

) for the two required and two optional floating-point value sets are

summarized in Table 2.3.2-A.

THE STRUCTURE OF THE JAVA VIRTUAL MACHINE Primitive Types and Values 2.3

Table 2.3.2-A. Floating-point value set parameters

Parameter float float-extended-

exponent

double double-extended-

exponent

N 24 24 53 53

K 8

≥ 11

≥ 15

max

+127

≥ +1023

+1023

≥ +16383

min

-126

≤ -1022

-1022

≤ -16382

Where one or both extended-exponent value sets are supported by an

implementation, then for each supported extended-exponent value set there is

a specific implementation-dependent constant K, whose value is constrained by

Table 2.3.2-A; this value K in turn dictates the values for E

min

and E

max

Each of the four value sets includes not only the finite nonzero values that are

ascribed to it above, but also the five values positive zero, negative zero, positive

infinity, negative infinity, and NaN.

Note that the constraints in Table 2.3.2-A are designed so that every element of the

float value set is necessarily also an element of the float-extended-exponent value

set, the double value set, and the double-extended-exponent value set. Likewise,

each element of the double value set is necessarily also an element of the double-

extended-exponent value set. Each extended-exponent value set has a larger range

of exponent values than the corresponding standard value set, but does not have

more precision.

The elements of the float value set are exactly the values that can be represented

using the single floating-point format defined in the IEEE 754 standard, except

that there is only one NaN value (IEEE 754 specifies 2

-2 distinct NaN values).

The elements of the double value set are exactly the values that can be represented

using the double floating-point format defined in the IEEE 754 standard, except

that there is only one NaN value (IEEE 754 specifies 2

-2 distinct NaN values).

Note, however, that the elements of the float-extended-exponent and double-

extended-exponent value sets defined here do not correspond to the values that

can be represented using IEEE 754 single extended and double extended formats,

respectively. This specification does not mandate a specific representation for the

values of the floating-point value sets except where floating-point values must be

represented in the class file format (§4.4.4, §4.4.5).

The float, float-extended-exponent, double, and double-extended-exponent value

sets are not types. It is always correct for an implementation of the Java Virtual

2.3 Primitive Types and Values THE STRUCTURE OF THE JAVA VIRTUAL MACHINE

Machine to use an element of the float value set to represent a value of type float;

however, it may be permissible in certain contexts for an implementation to use

an element of the float-extended-exponent value set instead. Similarly, it is always

correct for an implementation to use an element of the double value set to represent

a value of type double; however, it may be permissible in certain contexts for

an implementation to use an element of the double-extended-exponent value set

instead.

Except for NaNs, values of the floating-point value sets are ordered. When

arranged from smallest to largest, they are negative infinity, negative finite values,

positive and negative zero, positive finite values, and positive infinity.

Floating-point positive zero and floating-point negative zero compare as equal, but

there are other operations that can distinguish them; for example, dividing 1.0 by

0.0 produces positive infinity, but dividing 1.0 by -0.0 produces negative infinity.

NaNs are unordered, so numerical comparisons and tests for numerical equality

have the value false if either or both of their operands are NaN. In particular, a

test for numerical equality of a value against itself has the value false if and only

if the value is NaN. A test for numerical inequality has the value true if either

operand is NaN.

2.3.3 The returnAddress Type and Values

The returnAddress type is used by the Java Virtual Machine's jsr, ret, and jsr_w

instructions (§jsr, §ret, §jsr_w). The values of the returnAddress type are pointers

to the opcodes of Java Virtual Machine instructions. Unlike the numeric primitive

types, the returnAddress type does not correspond to any Java programming

language type and cannot be modified by the running program.

2.3.4 The boolean Type

Although the Java Virtual Machine defines a boolean type, it only provides

very limited support for it. There are no Java Virtual Machine instructions solely

dedicated to operations on boolean values. Instead, expressions in the Java

programming language that operate on boolean values are compiled to use values

of the Java Virtual Machine int data type.

The Java Virtual Machine does directly support boolean arrays. Its newarray

instruction (§newarray) enables creation of boolean arrays. Arrays of type

boolean are accessed and modified using the byte array instructions baload and

bastore (§baload, §bastore).

剩余617页未读，继续阅读

一萍之春

粉丝: 1
资源: 1

Java虚拟机规范9：深入解析Java SE 9 JVM

Java虚拟机规范_JavaSE 10

Java虚拟机规范_第9版_PR_EN

Java语言规范和JVM规范（7、8、9）

java虚拟机规范 (java se 7 中文版)

java虚拟机规范pdf

java虚拟机规范(java se 8版)

详细说明一下《Java虚拟机规范》这本书？请用中文描述，Use a temperature of 0.1

详细说明一下《Java虚拟机规范》这本书？请用中文描述，Use a temperature of 01

介绍一下Java虚拟机这本书？ Use a temperature of 1

在不同平台下java虚拟机的代码是基本一样的

最新资源