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apk安装报错：packageInfo is null？ - 用户反馈 - 清泛IT社区，为创新赋能！
编译设置问题，包名中没有英文点.，已修复，加了包名验证提示。
本地SQLite实现注册登录功能 - App Inventor 2 中文网 - 清泛IT社区，为创新赋能！
建表的SQL语句如下：
CREATE TABLE user(username TEXT PRIMARY KEY, password TEXT);
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最后提一下日志调试功能：
上面其实是用户密码信息，在日志控制台中能够输出便于调试查看。
Abstract class in Java
What is an "abstract class" in Java?
14 Answers
14
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Why is super.super.method(); not allowed in Java?
...e cases, perhaps you could overcome inor's objection with dynamic proxies (javahowto.blogspot.co.uk/2011/12/…), redirecting method calls to the original object (synchronizing variables after each call)? It seems that proxies require everything to be implementing an interface, though. Also, I won...
Is there anything like .NET's NotImplementedException in Java?
Is there anything like .NET's NotImplementedException in Java?
5 Answers
5
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PermGen elimination in JDK 8
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Fixed size at startup – difficult to tune.
Internal Hotspot types were Java objects : Could move with full GC, opaque, not strongly typed and hard to debug, needed meta-metadata.
Simplify full collections : Special iterators for metadata for each collector
Want to deallocate class data concurren...
Does Java have a complete enum for HTTP response codes?
I'm wondering if there is an enum type in some standard Java class library that defines symbolic constants for all of the valid HTTP response codes. It should support conversion to/from the corresponding integer values.
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How to create a directory in Java?
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As of Java 7, you should probably use the methods in Files as in the more recent answer by Benoit Blanchon. (This answer appears to have been written before Java 7.)
– Brick
Sep 8 '16 at 16:58...
What is the better API to Reading Excel sheets in java - JXL or Apache POI [closed]
...re are many differences:
Perhaps the most significant difference is that Java JXL does not support the Excel 2007+ ".xlsx" format; it only supports the old BIFF (binary) ".xls" format. Apache POI supports both with a common design.
Additionally, the Java portion of the JXL API was last updated in...
What is boxing and unboxing and what are the trade offs?
...e the expected metadata and structure that other data structures have.
In Java and Haskell generic collections can't contain unboxed values. Generic collections in .NET can hold unboxed values with no penalties. Where Java's generics are only used for compile-time type checking, .NET will generat...