Stackoverflow JAVA top100问题答案整理

た入场券 2022-06-15 12:37 216阅读 0赞

## 整理 ##

[stackoverflow-java-top-qa][] 是github上一个开源项目，但是将近一年没有更新了，我对它做了如下整理：  
1. 前阶段github的md文件编写方式更新，’\#’后面要接上空格才会有标题效果  
2. 对所有已翻译问题及其答案整理在一个[md文件][md]下，并导出[PDF][]  
**github地址：[https://github.com/linpeiyou/stackoverflow-java-top-qa][https_github.com_linpeiyou_stackoverflow-java-top-qa] 欢迎star**

## 问题目录 ##

> 基础语法

*  [Java += 操作符实质][Java _]
 *  [将InputStream转换为String][InputStream_String]
 *  [将数组转换为List][List]
 *  [如何遍历map对象][map]
 *  [public，protected，private，不加修饰符。有什么区别呢？][public_protected_private]
 *  [如何测试一个数组是否包含指定的值？][Link 1]
 *  [重写（Override）equlas和hashCode方法时应考虑的问题][Override_equlas_hashCode]
 *  [从一个多层嵌套循环中直接跳出][Link 2]
 *  [如何将String转换为Int][String_Int]
 *  [如何分割（split）string字符串][split_string]
 *  [在java中如何对比（compare）string][java_compare_string]
 *  [`Map<Key,Value>`基于Value值排序][Map_Key_Value_Value]
 *  [\`HashMap和Hashtable的区别][HashMap_Hashtable]
 *  [如何便捷地将两个数组合到一起][Link 3]
 *  [Java 是否支持默认的参数值][Java]
 *  [Java 产生指定范围的随机数][Java 1]
 *  [JavaBean 到底是什么][JavaBean]
 *  [wait()和sleep()的区别][wait_sleep]
 *  [能否在一个构造器( `constructor` )中调用另一个构造器][_constructor_]
 *  [ `finally` 代码块总会被执行么][_finally_]
 *  [如何将String转换为enum][String_enum]
 *  [在Java中声明数组][Java 2]
 *  [反射是什么及其用途][Link 4]
 *  [为什么不能用string类型进行switch判断][string_switch]
 *  [比较java枚举成员使用equal还是==][java_equal]
 *  [用java怎么创建一个文件并向该文件写文本内容][java]
 *  [serialVersionUID 有什么作用？该如何使用？][serialVersionUID]
 *  [为什么Java的`Vector`类被认为是过时的或者废弃的][Java_Vector]
 *  [Java的foreach循环是如何工作的][Java_foreach]
 *  [为什么相减这两个时间（1927年）会得到奇怪的结果][1927]
 *  [Java 中如何将 String 转换为 enum][Java _ String _ enum]
 *  [该什么时候使用 ThreadLocal变量，它是如何工作的][ThreadLocal]
 *  [servlets的运行原理][servlets]
 *  [如何计算MD5值][MD5]
 *  [Java中软引用和弱引用的区别][Java 3]
 *  [JSF, Servlet 和 JSP (三种技术)有什么区别][JSF_ Servlet _ JSP]
 *  [Java内部类和嵌套静态类][Java 4]
 *  [@Component, @Repository, @Service的区别][Component_ _Repository_ _Service]
 *  [如何创建泛型java数组][java 1]

> 编程技巧

*  [去掉烦人的“!=null”(判空语句][null]
 *  [获取完整的堆栈信息][Link 5]
 *  [如何用一行代码初始化一个ArrayList][ArrayList]
 *  [初始化静态map][map 1]
 *  [给3个布尔变量，当其中有2个或者2个以上为true才返回true][3_2_2_true_true]
 *  [输出 Java 数组最简单的方式][Java 5]
 *  [为什么以下用随机生成的文字会得出 “hello world”?][_hello world]
 *  [什么在java中存放密码更倾向于char\[\]而不是String][java_char_String]
 *  [如何避免在JSP文件中使用Java代码][JSP_Java]
 *  [Java 源码里的设计模式][Java 6]
 *  [如何产生一个随机的字母数字串作为 session 的唯一标识符][session]
 *  [如何创建单例][Link 6]
 *  [实现Runnable接口 VS. 继承Thread类][Runnable_ VS. _Thread]
 *  [我应该用哪一个@NotNull注解][NotNull]
 *  [怎样将堆栈追踪信息转换为字符串][Link 7]
 *  [如何处理 java.lang.outOfMemoryError PermGen space error][java.lang.outOfMemoryError PermGen space error]
 *  [如何在整数左填充0][0]
 *  [在调用 instanceof 前需要进行null检查吗][instanceof _null]
 *  [如何从文件里读取字符串][Link 8]
 *  [遍历集合时移除元素，怎样避免ConcurrentModificationException异常抛出][ConcurrentModificationException]
 *  [如何让IntelliJ编辑器永久性显示代码行数][IntelliJ]
 *  [如何使用maven把项目及其依赖打包为可运行jar包][maven_jar]

> 网络

*  [如何使用java.net.URLConnection接收及发送HTTP请求][java.net.URLConnection_HTTP]

> 性能

*  [LinkedList、ArrayList各自的使用场景，如何确认应该用哪一个呢？][LinkedList_ArrayList]
 *  [StringBuilder和StringBuffer有哪些区别呢][StringBuilder_StringBuffer]
 *  [为什么处理排序的数组要比非排序的快][Link 9]
 *  [如何使用Java创建一个内存泄漏的程序][Java 7]
 *  [为什么打印“B”会明显的比打印“\#”慢][B]

> 测试

*  [如何测试 private 方法，变量或者内部类][private]
 *  [JUnit4如何断言确定异常的抛出][JUnit4]

> Android

*  [在Android里面下载文件，并在ProgressDialog显示进度][Android_ProgressDialog]
 *  [如何获取Android设备唯一ID][Android_ID]
 *  [安装Android SDK的时候找不到JDK][Android SDK_JDK]

[stackoverflow-java-top-qa]: https://github.com/giantray/stackoverflow-java-top-qa
[md]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/%E6%B1%87%E6%80%BB/%E6%B1%87%E6%80%BB.md
[PDF]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/%E6%B1%87%E6%80%BB/%E6%B1%87%E6%80%BB.pdf
[https_github.com_linpeiyou_stackoverflow-java-top-qa]: https://github.com/linpeiyou/stackoverflow-java-top-qa
[Java _]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/java-operator.md
[InputStream_String]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/read-convert-an-inputstream-to-a-string.md
[List]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/create-arraylist-from-array.md
[map]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/iterate-through-a-hashmap.md
[public_protected_private]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/in-java-whats-the-difference-between-public-default-protected-and-private.md
[Link 1]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/how-can-i-test-if-an-array-contains-a-certain-value.md
[Override_equlas_hashCode]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/what-issues-should-be-considered-when-overriding-equals-and-hashcode-in-java.md
[Link 2]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/breaking-out-of-nested-loops-in-java.md
[String_Int]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/converting-string-to-int-in-java.md
[split_string]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/how-to-split-a-string-in-java.md
[java_compare_string]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/how-do-i-compare-strings-in-java.md
[Map_Key_Value_Value]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/how-to-sort-a-mapkey-value-on-the-values-in-java.md
[HashMap_Hashtable]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/differences-between-hashmap-and-hashtable.md
[Link 3]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/how-to-concatenate-two-arrays-in-java.md
[Java]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/does-java-support-default-parameter-values.md
[Java 1]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/generating-random-integers-in-a-range-with-Java.md
[JavaBean]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/what-is-a-javabean-exactly.md
[wait_sleep]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/difference-between-wait-and-sleep.md
[_constructor_]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/how-do-i-call-one-constructor-from-another-in-java.md
[_finally_]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/does-finally-always-execute-in-java.md
[String_enum]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/convert-a-string-to-an-enum-in-java.md
[Java 2]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/declare-array-in-java.md
[Link 4]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/what-is-reflection-and-why-is-it-useful.md
[string_switch]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/why-cant-i-switch-on-a-string.md
[java_equal]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/comparing-java-enum-members-or-equals.md
[java]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/how-to-create-a-file-and-write-to-a-file-in-java.md
[serialVersionUID]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/what-is-a-serialversionuid-and-why-should-i-use-it.md
[Java_Vector]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/why-is-java-vector-class-considered-obsolete-or-deprecated.md
[Java_foreach]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/how-does-the-java-for-each-loop-work.md
[1927]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/why-is-subtracting-these-two-times-in-1927-giving-a-strange-result.md
[Java _ String _ enum]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/lookup-enum-by-string-value.md
[ThreadLocal]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/when-and-how-should-i-use-a-threadlocal-variable.md
[servlets]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/how-do-servlets-work-instantiation-shared-variables-and-multithreading.md
[MD5]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/how-can-i-generate-an-md5-hash.md
[Java 3]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/what-is-the-difference-between-a-soft-reference-and-a-weak-reference-in-java.md
[JSF_ Servlet _ JSP]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/what-is-the-difference-between-jsf-servlet-and-jsp.md
[Java 4]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/java-inner-class-and-static-nested-class.md
[Component_ _Repository_ _Service]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/whats-the-difference-between-component-repository-service-annotations-in.md
[java 1]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/how-to-create-a-generic-array-in-java.md
[null]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/avoiding-null-statements-in-java.md
[Link 5]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/get-current-stack-trace-in-java.md
[ArrayList]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/initialization-of-an-arraylist-in-one-line.md
[map 1]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/how-can-i-initialize-a-static-map.md
[3_2_2_true_true]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/check-if-at-least-two-out-of-three-booleans-are-true.md
[Java 5]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/whats-the-simplest-way-to-print-a-java-array.md
[_hello world]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/why-does-this-code-using-random-strings-print-hello-world.md
[java_char_String]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/why-is-char-preferred-over-string-for-passwords-in-java.md
[JSP_Java]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/how-to-avoid-java-code-in-jsp-files.md
[Java 6]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/examples-of-gof-design-patterns-in-javas-core-libraries.md
[session]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/how-to-generate-a-random-alpha-numeric-string.md
[Link 6]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/what-is-an-efficient-way-to-implement-a-singleton-in-java.md
[Runnable_ VS. _Thread]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/implements-runnable-vs-extends-thread.md
[NotNull]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/which-notnull-java-annotation-should-i-use.md
[Link 7]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/how-can-i-convert-a-stack-trace-to-a-string.md
[java.lang.outOfMemoryError PermGen space error]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/dealing-with-java-lang-outofmemoryerror-permgen-space-error.md
[0]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/how-can-i-pad-an-integers-with-zeros-on-the-left.md
[instanceof _null]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/is-null-check-needed-before-calling-instanceof.md
[Link 8]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/how-do-i-create-a-java-string-from-the-contents-of-a-file.md
[ConcurrentModificationException]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/iterating-through-a-collection-avoiding-concurrentmodificationexception-when-reiterating-through-a-collection-avoiding-concurrentmodificationexception-when-re.md
[IntelliJ]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/how-can-i-permanently-have-line-numbers-in-intellij.md
[maven_jar]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/how-can-i-create-an-executable-jar-with-dependencies-using-maven.md
[java.net.URLConnection_HTTP]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/using-java-net-urlconnection-to-fire-and-handle-http-requests.md
[LinkedList_ArrayList]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/when-to-use-linkedlist-over-arraylist.md
[StringBuilder_StringBuffer]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/stringbuilder-and-stringbuffer.md
[Link 9]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/why-is-processing-a-sorted-array-faster-than-an-unsorted-array.md
[Java 7]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/creating-a-memory-leak-with-java.md
[B]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/why-is-printing-b-dramatically-slower-than-printing.md
[private]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/how-to-test-a-class-that-has-private-methods-fields-or-inner-classes.md
[JUnit4]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/how-do-you-assert-that-a-certain-exception-is-thrown-in-junit-4-tests.md
[Android_ProgressDialog]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/download-a-file-with-android-and-showing-the-progress-in-a-progressdialog.md
[Android_ID]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/is-there-a-unique-android-device-id.md
[Android SDK_JDK]: https://github.com/linpeiyou/stackoverflow-java-top-qa/blob/master/contents/android-sdk-installation-doesnt-find-jdk.md