A String object cannot be modified after it is created. (T/F)

The length of a String object s1 can be obtained using the expression s1 length. (T/F)

Given the code

String s1 = "yes" ;
String s2 = "yes" ;
String s3 = new String(s1) ;

Which of the following would equate to False ?

1. s1 == s2
2. s3 == s1
3. s1.equals(s2)
4. s3.equals(s1)

Suppose that s1 and s2 are two strings. Which of the statements or expressions are incorrect ?

1. String s3 = s1 + s2;
2. String s3 = s1 - s2;
3. s1.compareTo(s2);
4. int m = s1.length( );