Advanced timed challenge: In AP CSA, this item is specifically about Using Objects: object references, constructors, method calls, null references. What happens when String str = null; int n = str.indexOf("a"); is executed? Provide the solution as code.

Advanced timed challenge: In AP CSA, this item is specifically about Using Objects: object references, constructors, method calls, null references. Evaluate the expression "banana".substring(1, 4). What is the resulting String? Provide the solution as code.

Advanced timed challenge: In AP CSA, this item is specifically about Using Objects: object references, constructors, method calls, null references. Write an expression using the Math class to generate a random integer between 1 and 10, inclusive. Provide the solution as code.

Advanced timed challenge: In AP CSA, this item is specifically about Using Objects: object references, constructors, method calls, null references. If Car c1 = new Car(); Car c2 = c1;, changing c2.color will also change c1.color. Why? Provide the solution as code.

Advanced timed challenge: In AP CSA, this item is specifically about Using Objects: object references, constructors, method calls, null references. Given Rectangle r = new Rectangle(5, 10);, identify the constructor call and its parameters. Provide the solution as code.

Advanced timed challenge: In AP CSA, this item is specifically about Using Objects: object references, constructors, method calls, null references. Consider String s = "hello"; int len = s.length();. Identify the object reference and the method call. Provide the solution as code.