Is it possible to use double-quote characters as part of hashmap key?

I 开发者_JAVA技巧am going to have a string like "hello " world" as a hashmap key. The key is actually from user input, that's why it is possible to have something like that as a key. Is it okay?

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Absolutely. The double-quote character is only "special" as far as Java source code is concerned. You can even escape it within Java itself:

HashMap<String, String> map = new HashMap<String, String>();
map.put("foo\"bar", "value");
System.out.println(map.get("foo\"bar")); // Will print value

Here the key itself is foo"bar - the backslash is just for escaping within the string literal.

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Yes, of course. Even the 0-Character, which often is used as an End-of-String symbol in C is okey in Java, so there are really no constraints.

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Sure. If the key is of type String, then all characters are allowed. There is no limitation.

Just a reminder: assuming, the user enters:

 Jack"o"Lantern

then the Java literal is

 "Jack\"o\"Lantern"

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As the others told you, strings in java are allowed to contain all unicode characters, so for keys in a hashmap, you're fine.

But be careful when creating SQL queries, http requests or similar using strings which contain unfiltered user input - your software may be open to SQL injection or cross site scripting attacks then. Using mechanisms like prepared statements instead of string concatenation will help in this case.