"String str=new String("My String")" v.s. "String str="My String";

Question

-- what's the difference bet String str="My String"; to this
String str=new String("My String");

Answer 1

Its a subtle one. Its also been asked a hundred times before :-)
When a java class is compiled it "interns" all the Strings it can find.
Anywhere that you use that string, gets replaced with a reference to that string.
So the first gets a reference to the interned String.
The second creates a new String, using the interned String as an argument - results in reserving new memory.
Take this code:
String str1 = "My String";
String str2 = "My String";
String str3=  new String("My String");In effect the compiler turns it into something like this:
String internedString = "My String"
String str1 = internedString;
String str2 = internedString;
String str3 = new String(internedString);So initially, it only stores "MyString" once, and all your String variables point at that same memory space. As Strings are immutable in java (the contents never change) this is safe to do. str3 creates a NEW String, which reserves new memory, and copies the contents of internedString into it.
So
str1 == str2 (they point to the same bit of memory)
str1 != str3 (str3 created a new String, so is in new memory)
str1.equals(str3) (the contents of the strings are the same)
Hope this helps,
evnafets