Java:programmer's Boon

Why String class is Immutable ? Give some strong reasons behind this with examples.

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SPRING ARCHITECTURE

Does The following Code Compile
Giver Appropriate reason to suppor your answer..

class SampleCode
{
public static void main(String args[])
{
try{
System.out.println("SomeCode in try");
}
System.out.println("Some code in between");
catch(Exception exc)
{
exc.getMessage();
exc.printStackTrace();
}
}
}

The Singleton pattern, if used correctly is very helpful in designing complex systems.