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#LyX 2.2 created this file. For more info see http://www.lyx.org/
\lyxformat 508
\begin_document
\begin_header
\save_transient_properties true
\origin unavailable
\textclass ctex-book
\begin_preamble
\input{../../../writing-common/book-preamble.tex}
\end_preamble
\use_default_options true
\begin_modules
logicalmkup
coderemarks
tip-inset
note-inset
warning-inset
theorems-bytype
theorems-chap-bytype
\end_modules
\maintain_unincluded_children false
\language chinese-simplified
\language_package default
\inputencoding utf8-plain
\fontencoding global
\font_roman "default" "DejaVu Sans"
\font_sans "default" "DejaVu Serif"
\font_typewriter "default" "DejaVu Sans Mono"
\font_math "auto" "auto"
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\font_sc false
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\font_sf_scale 100 100
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\graphics default
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\bibtex_command default
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\use_package amsmath 1
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\cite_engine basic
\cite_engine_type default
\biblio_style plain
\use_bibtopic false
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\paperorientation portrait
\suppress_date false
\justification true
\use_refstyle 1
\boxbgcolor #dad3d7
\index Index
\shortcut idx
\color #008000
\end_index
\secnumdepth 3
\tocdepth 1
\paragraph_separation indent
\paragraph_indentation default
\quotes_language english
\papercolumns 1
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\tracking_changes false
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\end_header
\begin_body
\begin_layout Chapter
常见面试题
\end_layout
\begin_layout Standard
面试题往往比较“变态”，要求对Java的特性有深刻的理解才能给出正确答案。这里列出一些常见的面试题目，一方面加深对Java的理解，一方面未来可以更加从容的应对“
变态”的面试官们。
\end_layout
\begin_layout Section
方法的重载
\end_layout
\begin_layout Problem
给出
\begin_inset ERT
status open
\begin_layout Plain Layout
\backslash
lstlistingname
\end_layout
\end_inset
\begin_inset CommandInset ref
LatexCommand ref
reference "StaticDispatch.java"
\end_inset
\begin_inset CommandInset citation
LatexCommand cite
after "虚拟机字节码执行引擎"
key "jvm-advanced-feature"
\end_inset
的运行结果。
\begin_inset CommandInset include
LatexCommand lstinputlisting
filename "/home/subaochen/git/java-tutorial/guide/code/appendix/src/cn/edu/sdut/softlab/interview/StaticDispatch.java"
lstparams "caption={StaticDispatch.java},label={StaticDispatch.java}"
\end_inset
\end_layout
\begin_layout Problem
执行结果为：
\end_layout
\begin_layout Problem
\begin_inset Box Shaded
position "t"
hor_pos "c"
has_inner_box 1
inner_pos "t"
use_parbox 0
use_makebox 0
width "100col%"
special "none"
height "1in"
height_special "totalheight"
thickness "0.4pt"
separation "3pt"
shadowsize "4pt"
framecolor "black"
backgroundcolor "none"
status open
\begin_layout Plain Layout
hello, guy!
\end_layout
\begin_layout Plain Layout
hello, guy!
\end_layout
\begin_layout Plain Layout
hello, man!
\end_layout
\end_inset
\end_layout
\begin_layout Problem
本题重点考察两个方面：
\end_layout
\begin_layout Description
对象的类型 代码Human man = new Man()虽然通过new Man()创建了一个Man类型的对象，但是通过安全的“向上塑性”将这个Man类型的对象
转换为Human类型，因此man的数据类型是Human类型的。
\end_layout
\begin_layout Description
方法的重载是静态分派 即在编译阶段就确定了调用哪个重载的方法。javac在编译以上代码时，根据所传入参数的类型和数量来匹配应该调用哪个方法。本例中，前两次调用s
ayHello()方法均传递了Human类型的对象，因此实际调用的方法为sayHello(Human guy)，最后一次调用讲man对象强制转换为Man类型，因
此调用的是sayHello(Man guy）方法，这样就不难理解输出结果了。
\end_layout
\begin_layout Standard
我们可以通过分析StaticDispatch的Class文件结构
\begin_inset Foot
status open
\begin_layout Plain Layout
执行javap -verbose StaticDispatch查看完整的class文件结构
\end_layout
\end_inset
验证这一点（仅截取相关部分代码）：
\end_layout
\begin_layout Standard
\begin_inset listings
lstparams "basicstyle={\ttfamily},breaklines=true,showstringspaces=false"
inline false
status open
\begin_layout Plain Layout
......
\end_layout
\begin_layout Plain Layout
// 以下为main()方法的部分字节码
\end_layout
\begin_layout Plain Layout
23: astore_3
\end_layout
\begin_layout Plain Layout
24: aload_3
\end_layout
\begin_layout Plain Layout
25: aload_1
\end_layout
\begin_layout Plain Layout
26: invokevirtual #13 // Method sayHello:(Lcn/edu/sdut/softlab/interview/StaticD
ispatch$Human;)V
\end_layout
\begin_layout Plain Layout
29: aload_3
\end_layout
\begin_layout Plain Layout
30: aload_2
\end_layout
\begin_layout Plain Layout
// 调用的是参数为Human类型的sayHello方法
\end_layout
\begin_layout Plain Layout
31: invokevirtual #13 // Method sayHello:(Lcn/edu/sdut/softlab/interview/Static
Dispatch$Human;)V
\end_layout
\begin_layout Plain Layout
34: aload_3
\end_layout
\begin_layout Plain Layout
35: aload_1
\end_layout
\begin_layout Plain Layout
36: checkcast #7 // class cn/edu/sdut/softlab/interview/StaticDispatch$Man
\end_layout
\begin_layout Plain Layout
// 调用的是参数为Man类型的sayHello方法
\end_layout
\begin_layout Plain Layout
39: invokevirtual #14 // Method sayHello:(Lcn/edu/sdut/softlab/interview/Static
Dispatch$Man;)V
\end_layout
\begin_layout Plain Layout
42: return
\end_layout
\end_inset
\end_layout
\end_body
\end_document