why does a char + another char = a weird number

Here's the code snippet:

public static void main (String[]arg) 
{
    char ca = 'a' ; 
    char cb = 'b' ; 
    System.out.println (ca + cb) ; 
}

The output is:

195

Why is this the case? I woul开发者_如何学Cd think that 'a' + 'b' would be either "ab" , "12" , or 3.

Whats going on here?

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+ of two char is arithmetic addition, not string concatenation. You have to do something like "" + ca + cb, or use String.valueOf and Character.toString methods to ensure that at least one of the operands of + is a String for the operator to be string concatenation.

JLS 15.18 Additive Operators

If the type of either operand of a + operator is String, then the operation is string concatenation.

Otherwise, the type of each of the operands of the + operator must be a type that is convertible to a primitive numeric type, or a compile-time error occurs.

As to why you're getting 195, it's because in ASCII, 'a' = 97 and 'b' = 98, and 97 + 98 = 195.

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This performs basic int and char casting.

 char ch = 'a';
 int i = (int) ch;   
 System.out.println(i);   // prints "97"
 ch = (char) 99;
 System.out.println(ch);  // prints "c"

This ignores the issue of character encoding schemes (which a beginner should not worry about... yet!).

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As a note, Josh Bloch noted that it is rather unfortunate that + is overloaded for both string concatenation and integer addition ("It may have been a mistake to overload the + operator for string concatenation." -- Java Puzzlers, Puzzle 11: The Last Laugh). A lot of this kinds of confusion could've been easily avoided by having a different token for string concatenation.

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See also

• Is concatenating with an empty string to do a string conversion really that bad?

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I don't speak Java, but 195 is 97 + 98 = the ASCII codes for a and b. So obviously, ca and cb are interpreted as their integer values, probably because of the + addition which does not seem to lead to a string concatenation automatically.

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If you want to have a String as result of the + operator you have to use type String as operands.

You should write:

public static void main (String[]arg) 
{
    String ca = "a" ; 
    String cb = "b" ; 
    System.out.println (ca + cb) ; 
}

The + operator applied on char operands behaves as the arithmetic sum.

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The + operator doesn't operate over characters like it does over strings. What's happening here is that a and b are being cast to their integer ASCII codepoints - 97 and 98 - and then added together.