in java

Suppose that s$1$ and s$2$ are two strings. Which of the following statements or

expressions are incorrect?

String s $=$ "Welcome to Java";

String s$3=$ s$1+$ s$2$;

String s$3=$ s$1-$ s$2$;

s$1==$ s$2$;

s$1>=$ s$2$;

s$1.$compareTo$($s$2)$;

int i $=$ s$1.$length$()$;

char c $=$ s$1(0)$;

char c $=$ s$1.$charAt$($s$1.$length$())$;