Why String behaves like value type while using ==

want to know why String behaves like value type while using ==.

         String s1 = "Hello";
        String s2 = "Hello";
        Console.WriteLine(s1 == s2);// True(why? s1 and s2 are different)
        Console.WriteLine(s1.Equals(s2));//True
        StringBuilder a1 = new StringBuilder("Hi");
        StringBuilder a2 = new StringBuilder("Hi");
        Console.WriteLine(a1 == a2);//false
        Console.WriteLine(a1.Equals(a2));//true

StringBuilde开发者_StackOverflowr and String behaves differently with == operator. Thanks.

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Two different reasons;

• interning - since the "Hello" string(s) are compiled into the source, they are the same reference - check ReferenceEquals(s1,s2) - it will return true
• custom equality - string has equality operators (in particular, == / != (aka op_Equality / op_Inequality)

The StringBuilder version fails because:

• they aren't the same reference (these are regular managed objects created separately on the managed heap)
• StringBuilder doesn't have the operators

Call ToString() on each, and it gets more interesting:

• the two strings aren't the same reference
• but the operator support guarantees a true

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The == operator is overloaded in the String class, in a way that makes the string values to be compared instead of the object references, which is the default.

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Because == operator is redefined for strings.

See MSDN

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It's because the equality operator has been overridden to provide the functionality you see. You can do this on any type by overriding the equals operator.

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Using == for strings is bad practice anyways, just use Equals().

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