a.b.c.i = 0;
//下面是异常信息
Exception in thread "main" java.lang.NullPointerException
at Prog.main(Prog.java:5)
文件名和行号不能精确指出哪个变量为空。是a还是b或c?JDK14对此做了改进。
Exception in thread "main" java.lang.NullPointerException:
Cannot read field 'c' because 'a.b' is null.
at Prog.main(Prog.java:5)
但是,这也存在一些风险。空指针异常消息包含源代码中的变量名。暴露此信息可能被视为程序的安全风险。
三、switch表达式
在Java 14之前*
switch (day) {
case MONDAY:
case FRIDAY:
case SUNDAY:
System.out.println(6);
break;
case TUESDAY:
System.out.println(7);
break;
case THURSDAY:
case SATURDAY:
System.out.println(8);
break;
case WEDNESDAY:
System.out.println(9);
break;
}
Java 14增强功能
switch (day) {
case MONDAY, FRIDAY, SUNDAY -> System.out.println(6);
case TUESDAY -> System.out.println(7);
case THURSDAY, SATURDAY -> System.out.println(8);
case WEDNESDAY -> System.out.println(9);
}
final class Point {
public final int x;
public final int y;
public Point(int x, int y) {
this.x = x;
this.y = y;
}
// 很多的equals, hashCode, toString,getters、setters
}
使用Ant视图: 在我的Java或Debug模式下,我喜欢显示出Ant视图,这样我就可以迅速的运行Ant任务。通过Window Ant可以找到该视图。把Ant视图放在屏幕的一角, 通过“添加编译文件(Addà Other à Show View à Buildfiles)”按钮来添加build.xml文件。在3.1版本中,甚至支持Ant调试脚本语言。
Warning This feature was DEPRECATED in PHP 5.5.0, and REMOVED as of PHP 7.0.0.如果设置了这个被弃用的修饰符, preg_replace() 在进行了对替换字符串的 后向引用替换之后, 将替换后的字符串作为php 代码评估执行(eval 函数方式),并使用执行结果 作为实际参与替换的字符串。单引号、双引号、反斜线(\)和 NULL 字符在 后向引用替换时会被用反斜线转义.
This feature was DEPRECATED in PHP 5.5.0, and REMOVED as of PHP 7.0.0.如果设置了这个被弃用的修饰符, preg_replace() 在进行了对替换字符串的 后向引用替换之后, 将替换后的字符串作为php 代码评估执行(eval 函数方式),并使用执行结果 作为实际参与替换的字符串。单引号、双引号、反斜线(\)和 NULL 字符在 后向引用替换时会被用反斜线转义.
Google is reportedly planning to relaunch its search engine in China, complete with censored results to meet the demands of the Chinese government. The company originally shut down its Chinese search engine in 2010, citing government attempts to “limit free speech on the web.” But according to a report from The Intercept, the US tech giant now wants to return to the world’s biggest single market for internet users.
According to internal documents provided to The Intercept by a whistleblower, Google has been developing a censored version of its search engine under the codename “Dragonfly” since the beginning of 2017. The search engine is being built as an Android mobile app and will reportedly “blacklist sensitive queries” and filter out all websites blocked by China’s web censors (including Wikipedia and BBC News). The censorship will extend to Google’s image search, spell check, and suggested search features.
The web is heavily censored in China, with the country’s so-called Great Firewall stopping citizens from accessing many sites. Information on topics like religion, police brutality, freedom of speech, and democracy are heavily filtered, while specific search topics (like the 1989 Tiananmen Square protests and Taiwanese independence) are censored completely. Advocacy groups report that censorship in the country has increased under President Xi Jinping, extending beyond the web to social media and chat apps.
The whistleblower who spoke to The Intercept said they did so because they were “against large companies and governments collaborating in the oppression of their people.” They also suggested that “what is done in China will become a template for many other nations.”
Patrick Poon, a researcher with Amnesty International, agreed with this assessment. Poon told The Intercept that if Google launches a censored version of its search engine in China it will “set a terrible precedent” for other companies. “The biggest search engine in the world obeying the censorship in China is a victory for the Chinese government — it sends a signal that nobody will bother to challenge the censorship any more,” said Poon.
In a statement given to The Verge, a spokesperson said: “We provide a number of mobile apps in China, such as Google Translate and Files Go, help Chinese developers, and have made significant investments in Chinese companies like JD.com. But we don’t comment on speculation about future plans.”
According to The Intercept, Google faces a number of substantial barriers before it can launch its new search app in China, including approval from officials in Beijing and “confidence within Google” that the app will be better than its main rival in China, Baidu.
Google previously offered a censored version of its search engine in China between 2006 and 2010, before pulling out of the country after facing criticism in the US. (Politicians said the company was acting as a “functionary of the Chinese government.”) In recent months, though, the company has been attempting to reintegrate itself into the Chinese commercial market. It launched an AI research lab in Beijing last December, a mobile file management app in January, and an AI-powered doodle game just last month.
Although this suggests Google is eager to get a slice of China’s huge market of some 750 million web users, ambitions to relaunch its search engine may yet go nowhere. Reports in past years of plans to bring the Google Play mobile store to China, for example, have so far come to nothing, and Google regularly plans out projects it ultimately rejects.
Notably, relations between China and the US have worsened in recent weeks due to trade tariffs imposed by President Trump. The Intercept reports that despite this Google staff have been told to be ready to launch the app at short notice. The company’s search engine chief, Ben Gomes, reportedly told employees last month that they must be prepared in case “suddenly the world changes or [President Trump] decides his new best friend is Xi Jinping.”
“=========================================================================
” DesCRiption: 适合自己使用的vimrc文件,for Linux/Windows, GUI/Console
”
” Last Change: 2010年08月02日 15时13分
”
” Version: 1.80
”
“=========================================================================
set nocompatible ” 关闭 vi 兼容模式
syntax on ” 自动语法高亮
colorscheme molokai ” 设定配色方案
set number ” 显示行号
set cursorline ” 突出显示当前行
set ruler ” 打开状态栏标尺
set shiftwidth=4 ” 设定 << 和 >> 命令移动时的宽度为 4
set softtabstop=4 ” 使得按退格键时可以一次删掉 4 个空格
set tabstop=4 ” 设定 tab 长度为 4
set nobackup ” 覆盖文件时不备份
set autochdir ” 自动切换当前目录为当前文件所在的目录
filetype plugin indent on ” 开启插件
set backupcopy=yes ” 设置备份时的行为为覆盖
set ignorecase smartcase ” 搜索时忽略大小写,但在有一个或以上大写字母时仍保持对大小写敏感
set nowrapscan ” 禁止在搜索到文件两端时重新搜索
set incsearch ” 输入搜索内容时就显示搜索结果
set hlsearch ” 搜索时高亮显示被找到的文本
set noerrorbells ” 关闭错误信息响铃
set novisualbell ” 关闭使用可视响铃代替呼叫
set t_vb= ” 置空错误铃声的终端代码
” set showmatch ” 插入括号时,短暂地跳转到匹配的对应括号
” set matchtime=2 ” 短暂跳转到匹配括号的时间
set magic ” 设置魔术
set hidden ” 允许在有未保存的修改时切换缓冲区,此时的修改由 vim 负责保存
set guioptions-=T ” 隐藏工具栏
set guioptions-=m ” 隐藏菜单栏
set smartindent ” 开启新行时使用智能自动缩进
set backspace=indent,eol,start
” 不设定在插入状态无法用退格键和 Delete 键删除回车符
set cmdheight=1 ” 设定命令行的行数为 1
set laststatus=2 ” 显示状态栏 (默认值为 1, 无法显示状态栏)
set statusline=\ %<%F[%1*%M%*%n%R%H]%=\ %y\ %0(%{&fileformat}\ %{&encoding}\ %c:%l/%L%)\
” 设置在状态行显示的信息
set foldenable ” 开始折叠
set foldmethod=syntax ” 设置语法折叠
set foldcolumn=0 ” 设置折叠区域的宽度
setlocal foldlevel=1 ” 设置折叠层数为
” set foldclose=all ” 设置为自动关闭折叠
” nnoremap <space> @=((foldclosed(line(‘.’)) < 0) ? ‘zc’ : ‘zo’)<CR>
” 用空格键来开关折叠
” return OS type, eg: windows, or linux, mac, et.st..
function! MySys()
if has(“win16”) || has(“win32”) || has(“win64”) || has(“win95”)
return “windows”
elseif has(“unix”)
return “linux”
endif
endfunction
” 用户目录变量$VIMFILES
if MySys() == “windows”
let $VIMFILES = $VIM.’/vimfiles’
elseif MySys() == “linux”
let $VIMFILES = $HOME.’/.vim’
endif
” 设定doc文档目录
let helptags=$VIMFILES.’/doc’
” 设置字体 以及中文支持
if has(“win32″)
set guifont=Inconsolata:h12:cANSI
endif
” 配置多语言环境
if has(“multi_byte”)
” UTF-8 编码
set encoding=utf-8
set termencoding=utf-8
set formatoptions+=mM
set fencs=utf-8,gbk
if v:lang =~? ‘^zh\|ja\|ko‘
set ambiwidth=double
endif
if has(“win32”)
source $VIMRUNTIME/delmenu.vim
source $VIMRUNTIME/menu.vim
language messages zh_CN.utf-8
endif
else
echoerr “Sorry, this version of (g)vim was not compiled with +multi_byte”
endif
” Buffers操作快捷方式!
nnoremap <C-RETURN> :bnext<CR>
nnoremap <C-S-RETURN> :bprevious<CR>
” Tab操作快捷方式!
nnoremap <C-TAB> :tabnext<CR>
nnoremap <C-S-TAB> :tabprev<CR>
“关于tab的快捷键
” map tn :tabnext<cr>
” map tp :tabprevious<cr>
” map td :tabnew .<cr>
” map te :tabedit
” map tc :tabclose<cr>
“窗口分割时,进行切换的按键热键需要连接两次,比如从下方窗口移动
“光标到上方窗口,需要<c-w><c-w>k,非常麻烦,现在重映射为<c-k>,切换的
“时候会变得非常方便.
nnoremap <C-h> <C-w>h
nnoremap <C-j> <C-w>j
nnoremap <C-k> <C-w>k
nnoremap <C-l> <C-w>l
“一些不错的映射转换语法(如果在一个文件中混合了不同语言时有用)
nnoremap <leader>1 :set filetype=xhtml<CR>
nnoremap <leader>2 :set filetype=css<CR>
nnoremap <leader>3 :set filetype=javascript<CR>
nnoremap <leader>4 :set filetype=php<CR>
” set fileformats=unix,dos,mac
” nmap <leader>fd :se fileformat=dos<CR>
” nmap <leader>fu :se fileformat=unix<CR>
” use Ctrl+[l|n|p|cc] to list|next|previous|jump to count the result
” map <C-x>l <ESC>:cl<CR>
” map <C-x>n <ESC>:cn<CR>
” map <C-x>p <ESC>:cp<CR>
” map <C-x>c <ESC>:cc<CR>
” 让 Tohtml 产生有 CSS 语法的 html
” syntax/2html.vim,可以用:runtime! syntax/2html.vim
let html_use_css=1
” Python 文件的一般设置,比如不要 tab 等
autocmd FileType python set tabstop=4 shiftwidth=4 expandtab
autocmd FileType python map <F12> :!python %<CR>
” 选中状态下 Ctrl+c 复制
vmap <C-c> “+y
” 打开javascript折叠
let b:javascript_fold=1
” 打开javascript对dom、html和css的支持
let javascript_enable_domhtmlcss=1
” 设置字典 ~/.vim/dict/文件的路径
autocmd filetype javascript set dictionary=$VIMFILES/dict/javascript.dict
autocmd filetype css set dictionary=$VIMFILES/dict/css.dict
autocmd filetype php set dictionary=$VIMFILES/dict/php.dict
“—————————————————————–
” plugin – bufexplorer.vim Buffers切换
” \be 全屏方式查看全部打开的文件列表
” \bv 左右方式查看 \bs 上下方式查看
“—————————————————————–
“—————————————————————–
” plugin – taglist.vim 查看函数列表,需要ctags程序
” F4 打开隐藏taglist窗口
“—————————————————————–
if MySys() == “windows” ” 设定windows系统中ctags程序的位置
let Tlist_Ctags_Cmd = ‘”‘.$VIMRUNTIME.’/ctags.exe”‘
elseif MySys() == “linux” ” 设定windows系统中ctags程序的位置
let Tlist_Ctags_Cmd = ‘/usr/bin/ctags’
endif
nnoremap <silent><F4> :TlistToggle<CR>
let Tlist_Show_One_File = 1 ” 不同时显示多个文件的tag,只显示当前文件的
let Tlist_Exit_OnlyWindow = 1 ” 如果taglist窗口是最后一个窗口,则退出vim
let Tlist_Use_Right_Window = 1 ” 在右侧窗口中显示taglist窗口
let Tlist_File_Fold_Auto_Close=1 ” 自动折叠当前非编辑文件的方法列表
let Tlist_Auto_Open = 0
let Tlist_Auto_Update = 1
let Tlist_Hightlight_Tag_On_BufEnter = 1
let Tlist_Enable_Fold_Column = 0
let Tlist_Process_File_Always = 1
let Tlist_Display_Prototype = 0
let Tlist_Compact_Format = 1
“—————————————————————–
” plugin – mark.vim 给各种tags标记不同的颜色,便于观看调式的插件。
” \m mark or unmark the word under (or before) the cursor
” \r manually input a regular expression. 用于搜索.
” \n clear this mark (i.e. the mark under the cursor), or clear all highlighted marks .
” \* 当前MarkWord的下一个 \# 当前MarkWord的上一个
” \/ 所有MarkWords的下一个 \? 所有MarkWords的上一个
“—————————————————————–
“—————————————————————–
” plugin – NERD_tree.vim 以树状方式浏览系统中的文件和目录
” :ERDtree 打开NERD_tree :NERDtreeClose 关闭NERD_tree
” o 打开关闭文件或者目录 t 在标签页中打开
” T 在后台标签页中打开 ! 执行此文件
” p 到上层目录 P 到根目录
” K 到第一个节点 J 到最后一个节点
” u 打开上层目录 m 显示文件系统菜单(添加、删除、移动操作)
” r 递归刷新当前目录 R 递归刷新当前根目录
“—————————————————————–
” F3 NERDTree 切换
map <F3> :NERDTreeToggle<CR>
imap <F3> <ESC>:NERDTreeToggle<CR>