15. Suppose x1, y 2,2-3, then the value of the expression y + =2--/+ +* is ) A 3 B 3.5 C4 D. 5 16. In the following Java statement, String str = "123456789", str =str.substring(13) the value in str after execution ( A. "23" B. "123" C. "12" D. "234" 17. With the definition int i = 6, after executing the following statement, the value of it-i-1: A. 10 B 121 C. 11 D. 100 18. When is the constructor called A. When creating an object B. when defining a class C. when using the method of the object D. when using the properties of the object 19. The output result of the following program segment is int x 20, y=30: if(x>50&&y++<.60 system.out.println a. b c. d. after the following statement is executed value of i int iffi-1>) else A. 15 B. 16 C7 D. 8