C#

Reference types are nullable by default; in-language null keyword is untyped. Lack of discriminated unions Exceptions as default, non-exceptional error handling method - there's not much of an alternative. archaic switch statement syntax and limitations Needless distinction between constructors + static methods Static methods can't be part of an interface Lack of by-shape interface implementation rather than explicit interface implementation - leading to numerous language design hacks such as the linq query syntax, foreach, collection & object initializers -- none of which can be flexibly reused. For example, the object initializer syntax may be nice, but plays poorly with immutable objects. Cannot inherit "interface" of a class independently of implementation - leading to code duplications and overarchitected code that provides interfaces, abstract base classes, a few common implementations, and no way to pick and choose the bits of each to use. Also; leads to too many code that's tightly coupled to a particular implementation since it's common to explicitly refer to the implementation type rather than an interface. Cannot multiply inherit via composition since a classes "interface" is tightly coupled to it's implementation; effectively lack of mixins. The above limitations of interfaces lead to a proliferation of virtually identical interfaces that don't overlap naturally in any kind of type hierarchy. IComparable vs. IEquatable vs. IComparable<T> vs object.Equals vs. operator == etc. etc. By extension, making a custom type that satisfies all these things is a lot more work than necessary (in particular for collection classes). Obviously, the language designers realize this, hence the various workarounds for things like linq, foreach and collection initializers which work by-shape rather than by-interface. Redundant use of parentheses and braces rather than layout-is-structure. Return values can be ignored, limiting the effectiveness of type inference. Enums aren't a normal type and can't have methods. Also, enum values aren't typesafe and may be initialized to 0 despite not having a 0 value. Mixing metaphors by lumping flag and non-flag enums together. Lack of proper value type support. Value types can't be inherited, have different constructor semantics, and perform poorly due to CLR limitations. Also, confusing semantics regarding value types: some values are really values (and can't be modified), and others are really non-aliased, non-null references (variables). This gets particularly confusing with regards to the next issue: Semantic distinction between fields and properties, particularly in conjunction with lack of mutability modifier (ala C++'s const) Can't specialize generics Cannot provide default generic type parameters (e.g. factory generics) lack of typedef makes generics a pain to use (using is a limited but good-to-know substitute!) Can't genericize over things other than types (e.g. functions, plain values, or names). This means you can't do something like make a generic implementation of a dependancy property leading to, well, nasty implementations of things like dependancy properties and the overuse of code-snippets and poorly readable code as a result. Limited capability to specify generic type requirements e.g. generic sum method that takes both int, double and a bigint (without tricky and often slow hacks). An interface method implementation or virtual method override cannot return a more specific type or accept a more general type; i.e. limited co/contravariance support even in C# 4.

JavaScript:

The Object prototype can be modified. Every single object in your program gets new properties, and something probably breaks. All objects are hash maps, but it's difficult to safely use them as such. In particular, if one of your keys happens to be __proto__, you're in trouble. No object closure at function reference time. In fact, no object closure at all -- instead, this is set whenever a function is called with object notation or the new operator. Results in much confusion, particularly when creating event callbacks, because this isn't set to what the programmer expects. Corollary: calling a function without object notation or the new operator results in this being set equal to the global object, resulting in much breakage. Addition operator overloaded to also perform string concatenation, despite the two operations being fundamentally different. Results in pain when a value you expect to be a number is in fact a string. == and != operators perform type coercion. Comparisons between different types involve a list of rules that no mortal can remember in full. This is mitigated by the existence of === and !== operators. Both null and undefined exist, with subtly different, yet redundant meanings. Why? Weird syntax for setting up prototype chains. parseInt(s) expects a C-style number, so treats values with leading zeroes as octal, etc. You can at least parseInt(s, 10) but the default behaviour is confusing. No block scope. Can declare the same variable more than once. Can use a variable without declaring it, in which case it's global and probably breaks your program. with { }. Really difficult to document with JavaDoc like tools.

JavaFX

Type inference sometimes doesn't behave like you would expect, so you often need to explicitly declare the type. def behaves likes const in C and not final in Java you can insert a value in a sequence by accessing an index >= seq.length, which should actually throw a compiler error (according to the reference). if you assign null to a String, it defaults to "". If you assign null to an Integer, a compiler error is thrown (in contrast to what the reference says). handles CheckedExceptions the same way as RuntimeExceptions

Perl

我喜欢这门语言，我不想添加已经被使用过的东西，但还没有人提到过这一点，所以我就把它扔到锅上。当我使用这个特性时，我发现这是我一生中最可怕的经历(而且我用过汇编语言):

write()和format()函数。

它们的语法是最糟糕、最丑陋、最可怕的，但是它们并没有提供比printf()更好的功能更多的功能。任何人都不应该尝试使用这两个函数进行任何输出，因为它们有多糟糕。

我相信有人会不同意，但是当我研究它们，希望它们能解决我的问题时，我发现它们是一个“痛苦的世界”(引用Big Lebowski的话)，我希望Perl6已经消除了它们，或者更好的是完全重写它们，使它们在某种程度上更可用和有用。

我知道我迟到了，但恨是永恒的!

Java

Runtime.exec(). So, if I don't manually clear the STDOUT and STDERR buffers, my code will hang? Wow. Die, plz. Null Pointer Exceptions. Responsible programming means I have to treat most objects like they're unexploded bombs, which is kind of a pisser in an object-oriented language. And when the inevitable happens I kinda need to know which object blew up in my face, but Java apparently feels telling me would be cheating. File I/O. Why do I have to jump through this many hoops to read a dang text file? And when copying files, I have to funnel the source file into my code and manually handle the output byte buffer? You're serious? Primitives vs. Primitive Wrappers. Note that Java now has a number of features that allow you to treat primitives and their wrapper objects as interchangeable in some places, but not in others; don't worry, the compiler will let you know which is which. This feels like a hack to work around a fundamentally broketastic design decision. And it is. (EDIT: Actually, the compiler is a much crappier safety net than I thought, particular when doing equality checks. If `a` and `b` are integers, `a == b` is guaranteed to behave as expected only if at least one of them is of type `int`. If they're both type `Integer`, then that statement will do what you think only if the two numbers are between -128 and 127. `Integer a = 1000; Integer b = 1000; return a == b;` will return `false`. Really.) XML. I have this dirt-simple little XML file I need to create and I have to do what?

.NET框架(库)

嵌套类型很少使用(例如MessageBoxButton应该是MessageBox.Button) 可变结构体(Rect, Point) 系统名称空间中有太多东西 太多不同的平等概念(对象。等于,对象。ReferenceEquals, operator ==， operator !=， IComparable.CompareTo() == 0) 数组的成员是可变的，但长度是不变的。

还有一点:

XmlSerialization不适用于不可变类型