merge

README.md

@@ -1,28 +1,33 @@
+
 stackoverflow-Java-top-qa
 =======================
     对stackoverflow上Java相关、投票数TOP100的问答进行翻译，欢迎点star，我们会持续更新!!!
 
     为了让“翻译”更有意义，给阅读者带来更多、更有效的收获，我们会有一些加工：
     例如，对问题进行分类，整合多个答案、删除冗余内容、加上自己的验证结果、心得等等
-
+    
     对于参与翻译的人，这也是很好的一个学习、理解过程，欢迎大家一起来翻译
 
 -------------
 ### 如何参与翻译（欢迎加入翻译组QQ群485011036）
-如何参与：
-- 请从下文“待翻译问题链接”中寻找你感兴趣的问答进行翻译。翻译好的问答，放到contents目录下，无需更新readme.md文档。之后提一个PR，我会对你的翻译做一个审校，并更新到readme中。
+####如何参与：
+- 请从下文“待翻译问题链接”中寻找你感兴趣的问答进行翻译。翻译好的问答，放到contents目录下，无需更新readme.md文档。之后提一个PR，我负责合并PR并更新到readme中。
 - 另外，为了避免多人重复新翻译一个问题，你可以提issue，说明你计划翻译的问题及时间点，我可以先更新到下面的”未翻译问题“中，说明已有人领了这个问题。当然，也不一定要提issue，一般情况下，只要及时提pr，我及时审核，出现”撞车“的概率并不高。
 
-一些基本的约定：
+####一些基本的约定：
 - 文档的文件名，和stackoverflowhich-notnull-java-annotation-should-i-usew上的url保持一致。例如，http://stackoverflow.com/questions/8710619/java-operator 的文件名， 就是java-operator.md
 - 在每篇翻译文档内容的最后，要附上stackoverflow的原文链接
 
-每个人可以做（但不限于）：
+####每个人可以做（但不限于）：
 - 找未翻译的问题进行翻译
 - 优化已翻译的问题
 - 输出问答精简汇总版（把所有的问答集中到一个md文件，然后尽量精简，让别人可以在一天内把这100个问题的精髓都看完）
 - 输出gitbook版本（现在直接在github上查看，体验不好）
 
+####文档优化反馈：
+请大家多多反馈，优化已翻译好的文章：可以到[吐槽区](https://github.com/giantray/stackoverflow-java-top-qa/issues/66)吐槽，也可以在已翻译文章基础上进行优化，提新的PR。文章质量的提升，需要大家一起努力！
+
+
 ### 目录
 > 基础语法
 
@@ -53,6 +58,18 @@ stackoverflow-Java-top-qa
 * [比较java枚举成员使用equal还是==](https://github.com/giantray/stackoverflow-java-top-qa/blob/master/contents/comparing-java-enum-members-or-equals.md)
 * [用java怎么创建一个文件并向该文件写文本内容](https://github.com/giantray/stackoverflow-java-top-qa/blob/master/contents/how-to-create-a-file-and-write-to-a-file-in-java.md)
 * [serialVersionUID 有什么作用？该如何使用？](https://github.com/giantray/stackoverflow-java-top-qa/blob/master/contents/what-is-a-serialversionuid-and-why-should-i-use-it.md)
+* [为什么Java的```Vector```类被认为是过时的或者废弃的](https://github.com/giantray/stackoverflow-java-top-qa/blob/master/contents/why-is-java-vector-class-considered-obsolete-or-deprecated.md)
+* [Java的foreach循环是如何工作的](https://github.com/giantray/stackoverflow-java-top-qa/blob/master/contents/how-does-the-java-for-each-loop-work.md)
+* [为什么相减这两个时间（1927年）会得到奇怪的结果](/contents/why-is-subtracting-these-two-times-in-1927-giving-a-strange-result.md)
+* [Java 中如何将 String 转换为 enum](/contents/lookup-enum-by-string-value.md)
+* [该什么时候使用 ThreadLocal变量，它是如何工作的](/contents/when-and-how-should-i-use-a-threadlocal-variable.md)
+* [servlets的运行原理](/contents/how-do-servlets-work-instantiation-shared-variables-and-multithreading.md)
+* [如何计算MD5值](/contents/how-can-i-generate-an-md5-hash.md)
+* [Java中软引用和弱引用的区别](/contents/what-is-the-difference-between-a-soft-reference-and-a-weak-reference-in-java.md)
+* [JSF, Servlet 和 JSP (三种技术)有什么区别](/contents/what-is-the-difference-between-jsf-servlet-and-jsp.md)
+* [Java内部类和嵌套静态类](/contents/java-inner-class-and-static-nested-class.md)
+* [@Component, @Repository, @Service的区别](/contents/whats-the-difference-between-component-repository-service-annotations-in.md)
+* [如何创建泛型java数组](/contents/how-to-create-a-generic-array-in-java.md)
 
 > 编程技巧
 
@@ -72,7 +89,12 @@ stackoverflow-Java-top-qa
 * [我应该用哪一个@NotNull注解](https://github.com/giantray/stackoverflow-java-top-qa/blob/master/contents/which-notnull-java-annotation-should-i-use.md)
 * [怎样将堆栈追踪信息转换为字符串](https://github.com/giantray/stackoverflow-java-top-qa/blob/master/contents/how-can-i-convert-a-stack-trace-to-a-string.md)
 * [如何处理 java.lang.outOfMemoryError PermGen space error](https://github.com/giantray/stackoverflow-java-top-qa/blob/master/contents/dealing-with-java-lang-outofmemoryerror-permgen-space-error.md)
-
+* [如何在整数左填充0](https://github.com/giantray/stackoverflow-java-top-qa/blob/master/contents/how-can-i-pad-an-integers-with-zeros-on-the-left.md)
+* [在调用 instanceof 前需要进行null检查吗](https://github.com/giantray/stackoverflow-java-top-qa/blob/master/contents/is-null-check-needed-before-calling-instanceof.md)
+* [如何从文件里读取字符串](/contents/how-do-i-create-a-java-string-from-the-contents-of-a-file.md)
+* [遍历集合时移除元素，怎样避免ConcurrentModificationException异常抛出](/contents/iterating-through-a-collection-avoiding-concurrentmodificationexception-when-reiterating-through-a-collection-avoiding-concurrentmodificationexception-when-re.md)
+* [如何让IntelliJ编辑器永久性显示代码行数](/contents/how-can-i-permanently-have-line-numbers-in-intellij.md)
+* [如何使用maven把项目及其依赖打包为可运行jar包](/contents/how-can-i-create-an-executable-jar-with-dependencies-using-maven.md)
 
 > 网络
 
@@ -83,64 +105,46 @@ stackoverflow-Java-top-qa
 * [LinkedList、ArrayList各自的使用场景，如何确认应该用哪一个呢？](https://github.com/giantray/stackoverflow-java-top-qa/blob/master/contents/when-to-use-linkedlist-over-arraylist.md)
 * [StringBuilder和StringBuffer有哪些区别呢](https://github.com/giantray/stackoverflow-java-top-qa/blob/master/contents/stringbuilder-and-stringbuffer.md)
 * [为什么处理排序的数组要比非排序的快](https://github.com/giantray/stackoverflow-java-top-qa/blob/master/contents/why-is-processing-a-sorted-array-faster-than-an-unsorted-array.md)
+* [如何使用Java创建一个内存泄漏的程序](https://github.com/giantray/stackoverflow-java-top-qa/blob/master/contents/creating-a-memory-leak-with-java.md)
+* [为什么打印“B”会明显的比打印“#”慢](https://github.com/giantray/stackoverflow-java-top-qa/blob/master/contents/why-is-printing-b-dramatically-slower-than-printing.md)
 
 > 测试
 
 * [如何测试 private 方法，变量或者内部类](https://github.com/giantray/stackoverflow-java-top-qa/blob/master/contents/how-to-test-a-class-that-has-private-methods-fields-or-inner-classes.md)
+* [JUnit4如何断言确定异常的抛出](/contents/how-do-you-assert-that-a-certain-exception-is-thrown-in-junit-4-tests.md)
 
 > Android
 
 * [在Android里面下载文件，并在ProgressDialog显示进度](https://github.com/giantray/stackoverflow-java-top-qa/blob/master/contents/download-a-file-with-android-and-showing-the-progress-in-a-progressdialog.md)
 * [如何获取Android设备唯一ID](https://github.com/giantray/stackoverflow-java-top-qa/blob/master/contents/is-there-a-unique-android-device-id.md)
+* [安装Android SDK的时候找不到JDK](contents/android-sdk-installation-doesnt-find-jdk.md)
 
 ### 待翻译问题链接(还剩x问题)
-- [Why is subtracting these two times (in 1927) giving a strange result?](http://stackoverflow.com/questions/6841333/why-is-subtracting-these-two-times-in-1927-giving-a-strange-result)
 - [Proper use cases for Android UserManager.isUserAGoat()?](http://stackoverflow.com/questions/13375357/proper-use-cases-for-android-usermanager-isuseragoat)
-- [Creating a memory leak with Java [closed]](http://stackoverflow.com/questions/6470651/creating-a-memory-leak-with-java) 用户AutumnLight正在翻译该问题
-- [Why is printing “B” dramatically slower than printing “#”?](http://stackoverflow.com/questions/21947452/why-is-printing-b-dramatically-slower-than-printing)
-- [How can I create an executable jar with dependencies using Maven?](http://stackoverflow.com/questions/574594/how-can-i-create-an-executable-jar-with-dependencies-using-maven)
 - [Why is executing Java code in comments with certain Unicode characters allowed?](http://stackoverflow.com/questions/30727515/why-is-executing-java-code-in-comments-with-certain-unicode-characters-allowed)
 - [Convert a String to an enum in Java](http://stackoverflow.com/questions/604424/convert-a-string-to-an-enum-in-java)
-- [Android SDK installation doesn't find JDK](http://stackoverflow.com/questions/4382178/android-sdk-installation-doesnt-find-jdk)
-- [Java inner class and static nested class](http://stackoverflow.com/questions/70324/java-inner-class-and-static-nested-class)
 - ['Must Override a Superclass Method' Errors after importing a project into Eclipse](http://stackoverflow.com/questions/1678122/must-override-a-superclass-method-errors-after-importing-a-project-into-eclips)
 - [Fastest way to determine if an integer's square root is an integer](http://stackoverflow.com/questions/295579/fastest-way-to-determine-if-an-integers-square-root-is-an-integer)
 - [How to fix: Unsupported major.minor version 51.0 error?](http://stackoverflow.com/questions/10382929/how-to-fix-unsupported-major-minor-version-51-0-error)
 - [How to generate a random alpha-numeric string?](http://stackoverflow.com/questions/41107/how-to-generate-a-random-alpha-numeric-string)
-- [Comparing Java enum members: == or equals()?](http://stackoverflow.com/questions/1750435/comparing-java-enum-members-or-equals)
 - [Failed to load the JNI shared Library (JDK)](http://stackoverflow.com/questions/7352493/failed-to-load-the-jni-shared-library-jdk)
-- [How to create a Java String from the contents of a file?](http://stackoverflow.com/questions/326390/how-to-create-a-java-string-from-the-contents-of-a-file)
-- [How do you assert that a certain exception is thrown in JUnit 4 tests?](http://stackoverflow.com/questions/156503/how-do-you-assert-that-a-certain-exception-is-thrown-in-junit-4-tests)
 - [What exactly is Apache Camel?](http://stackoverflow.com/questions/8845186/what-exactly-is-apache-camel)
-- [How can I permanently have line numbers in IntelliJ?](http://stackoverflow.com/questions/13751/how-can-i-permanently-have-line-numbers-in-intellij)
-- [How do servlets work? Instantiation, shared variables and multithreading](http://stackoverflow.com/questions/3106452/how-do-servlets-work-instantiation-shared-variables-and-multithreading)
 - [Access restriction on class due to restriction on required library rt.jar?](http://stackoverflow.com/questions/860187/access-restriction-on-class-due-to-restriction-on-required-library-rt-jar)
 - [How do I discover memory usage of my application in Android?](http://stackoverflow.com/questions/2298208/how-do-i-discover-memory-usage-of-my-application-in-android)
-- [How can I generate an MD5 hash?](http://stackoverflow.com/questions/415953/how-can-i-generate-an-md5-hash)
 - [Uncatchable ChuckNorrisException](http://stackoverflow.com/questions/13883166/uncatchable-chucknorrisexception)
 - [Can I add jars to maven 2 build classpath without installing them?](http://stackoverflow.com/questions/364114/can-i-add-jars-to-maven-2-build-classpath-without-installing-them)
 - [Update Eclipse with Android development tools v. 23](http://stackoverflow.com/questions/24437564/update-eclipse-with-android-development-tools-v-23)
 - [Setting multiple jars in java classpath](http://stackoverflow.com/questions/219585/setting-multiple-jars-in-java-classpath)
-- [Iterating through a list, avoiding ConcurrentModificationException when removing in loop](http://stackoverflow.com/questions/223918/iterating-through-a-list-avoiding-concurrentmodificationexception-when-removing)
-- [Is null check needed before calling instanceof](http://stackoverflow.com/questions/2950319/is-null-check-needed-before-calling-instanceof)
-- [How does the Java for each loop work?](http://stackoverflow.com/questions/85190/how-does-the-java-for-each-loop-work)
 - [What is the Java equivalent for LINQ?](http://stackoverflow.com/questions/1217228/what-is-the-java-equivalent-for-linq)
 - [Hibernate hbm2ddl.auto possible values and what they do?](http://stackoverflow.com/questions/438146/hibernate-hbm2ddl-auto-possible-values-and-what-they-do)
-- [How to round a number to n decimal places in Java](http://stackoverflow.com/questions/153724/how-to-round-a-number-to-n-decimal-places-in-java)
 - [How can I pad an integers with zeros on the left?](http://stackoverflow.com/questions/473282/how-can-i-pad-an-integers-with-zeros-on-the-left)
 - [Sort ArrayList of custom Objects by property](http://stackoverflow.com/questions/2784514/sort-arraylist-of-custom-objects-by-property)
-- [What's the difference between @Component, @Repository & @Service annotations in Spring?](http://stackoverflow.com/questions/6827752/whats-the-difference-between-component-repository-service-annotations-in)
-- [Why is Java Vector class considered obsolete or deprecated?](http://stackoverflow.com/questions/1386275/why-is-java-vector-class-considered-obsolete-or-deprecated)
 - [Efficiency of Java “Double Brace Initialization”?](http://stackoverflow.com/questions/924285/efficiency-of-java-double-brace-initialization)
 - [Why does this go into an infinite loop?](http://stackoverflow.com/questions/3831341/why-does-this-go-into-an-infinite-loop)
-- [When and how should I use a ThreadLocal variable?](http://stackoverflow.com/questions/817856/when-and-how-should-i-use-a-threadlocal-variable)
 - [decompiling DEX into Java sourcecode](http://stackoverflow.com/questions/1249973/decompiling-dex-into-java-sourcecode)
-- [How to create a generic array in Java?](http://stackoverflow.com/questions/529085/how-to-create-a-generic-array-in-java)
 - [Why does Math.round(0.49999999999999994) return 1](http://stackoverflow.com/questions/9902968/why-does-math-round0-49999999999999994-return-1)
 - [Eclipse: Set maximum line length for auto formatting?](http://stackoverflow.com/questions/3697287/eclipse-set-maximum-line-length-for-auto-formatting)
-- [What is the difference between a soft reference and a weak reference in Java?](http://stackoverflow.com/questions/299659/what-is-the-difference-between-a-soft-reference-and-a-weak-reference-in-java)
 - [What is the equivalent of the C++ Pair<L,R> in Java?](http://stackoverflow.com/questions/156275/what-is-the-equivalent-of-the-c-pairl-r-in-java)
-- [What is the difference between JSF, Servlet and JSP?](http://stackoverflow.com/questions/2095397/what-is-the-difference-between-jsf-servlet-and-jsp)
 - [How do I “decompile” Java class files?](http://stackoverflow.com/questions/272535/how-do-i-decompile-java-class-files)
 - [Useful Eclipse Java Code Templates [closed]](http://stackoverflow.com/questions/1028858/useful-eclipse-java-code-templates)
 - [How to call SOAP web service in Android](http://stackoverflow.com/questions/297586/how-to-call-soap-web-service-in-android)

SUMMARY.md

@@ -0,0 +1 @@
+\# Summary* [前言](README.md)

contents/android-sdk-installation-doesnt-find-jdk.md

@@ -0,0 +1,33 @@
+##安装Android SDK的时候找不到JDK
+
+###问题
+我在我的win7 64位的系统上安装Android SDK时，jdk-6u23-windows-x64.exe已经安装上了，但是Android SDK的安装程序却因为找不到已安装的JDK无法继续下去。
+这个问题出现过吗？有没有办法解决呢？
+
+![](http://ww2.sinaimg.cn/large/0060lm7Tgw1f72ny3m6oaj30ds0a0gmi.jpg)
+
+###回答1：
+当你看到这个提示（找不到jdk）的时候按Back（返回），然后再点Next(下一步)。这个时候，它将会去寻找JDK
+
+###回答2：
+实际安装：
+
+	- 系统：windows 8.1
+	- JDK文件： jdk-8u11-windows-x64.exe
+	- ADT文件：installer_r23.0.2-windows.exe
+安装64位JDK，然后尝试第一个回答中的back-next的方法。然后尝试设置JAVA_HOME 根据错误信息的提示，但是，仍旧对我没有用处，然后，尝试如下解决办法：
+
+按照它说的做，设置JAVA_HOME在你的系统环境变量中，这个路径要使用正斜杠(/)而非反斜杠(\)
+
+**注意：**
+当我把JAVA_HOME设置为C:\Program Files\Java\jdk1.6.0_31的时候还是不行，但是当我设置成C:/Program Files/Java/jdk1.6.0_31的时候就ok了。快把我逼疯了。
+
+如果还不行，就把 %JAVA_HOME%加在环境变量Path的头部。
+
+下面是我的环境变量的配置：
+	- JAVA_HOME=C:/Program Files/Java/jdk1.8.0_11
+	- JRE_HOME=C:/Program Files/Java/jre8
+	- Path=%JAVA_HOME%;C:...
+
+stackoverflow链接：
+http://stackoverflow.com/questions/4382178/android-sdk-installation-doesnt-find-jdk

contents/avoiding-null-statements-in-java.md

@@ -50,7 +50,8 @@ public interface Parser {
 
 我们来改造一下
 
-类定义如下，这样定义findAction方法后，确保无论用户输入什么，都不会返回null对象
+类定义如下，这样定义findAction方法后，确保无论用户输入什么，都不会返回null对象：
+```java
 public class MyParser implements Parser {
   private static Action DO_NOTHING = new Action() {
     public void doSomething() { /* do nothing */ }
@@ -62,7 +63,7 @@ public class MyParser implements Parser {
       return DO_NOTHING;
     }
   }}
-
+```
 
 对比下面两份调用实例
 1. 冗余:  每获取一个对象，就判一次空
@@ -74,7 +75,8 @@ if (parser == null) {
 }
 Action action = parser.findAction(someInput);
 if (action == null) {
-  // do nothing} else {
+  // do nothing} 
+else {
   action.doSomething();}
 ```
 
@@ -90,11 +92,11 @@ ParserFactory.getParser().findAction(someInput).doSomething();
 - 如果要用equal方法，请用object<不可能为空>.equal(object<可能为空>))
 例如：
 使用
-"bar".equals(foo) 
+`"bar".equals(foo) `
 而不是
-foo.equals("bar") 
+`foo.equals("bar") `
 - Java8或者guava lib中，提供了Optional类，这是一个元素容器，通过它来封装对象，可以减少判空。不过代码量还是不少。不爽。
-- 如果你想返回null，请挺下来想一想，这个地方是否更应该抛出一个异常
+- 如果你想返回null，请停下来想一想，这个地方是否更应该抛出一个异常
 
 stackoverflow链接：
-http://stackoverflow.com/questions/271526/avoiding-null-statements-in-java?page=2&tab=votes#tab-top
+http://stackoverflow.com/questions/271526/avoiding-null-statements-in-java?page=2&tab=votes#tab-top