Java please help ASAP! You dont need to test your code. I will give you a thumb up if you help me

1. [4pts] Name one important difference between an abstract class and an interface. 2. [4pts] Why are we guaranteed that every instance of every class will have certain methods like toString and equals? 3. [4pts] Explain the issue with the following code. How would you fix it without changing the first line? You are welcome to add lines of code. Object s = "Hello there"; System.out.println(s.substring(3))