You will write a number of recursive methods. Create a P11 project and class - you will implement the following interface: IP11.java There is no input file.

//IP11.java

import java.util.ArrayList; 

public interface IP11 { /* Method: printPattern Precondition: n>0 Postcondition: Print a pattern of n+1 ( 0 to n ) lines Postcondition: line i (i = 0 to n) has i stars ("*") followed by (n-i) stripes ("-") */ public void printPattern(int n); /* Method: convertNum Precondition: num.length > 0 Postcondition: return int representation of num, (e.g num:{1,2,3} returns int: 123) */ public int convertNum(int[] num); /* Method intersection Precondition: AL1 and AL2 are not empty Precondition: The elements in AL1 are unique within AL1 Precondition: The elements in AL2 are unique within AL2 (but AL1 and AL2 can contain the same elements) Postcondition: return an ArrayList with elements that are in both AL1 and AL2 *** in the order they occur in AL1 *** Postcondition: The elements in AL1 and AL2 are unchanged. */ public ArrayList intersection( ArrayList AL1, ArrayList AL2); } 

P11 is the only class in this assignment. You can exercise your methods more by extending the main method. We will test your code using a testClient class. Do not change the signature of the specified methods. You can however, and are advised to, create your own helper methods.

You will use ***RECURSION ONLY*** in this assignment, i.e., there will be no loops in any of the methods you implement. Any programs with loops found in them will be given a zero. Here are the methods in P11 that you will implement.

void printPattern(int n)

Precondition: n>0 Postcondition: print a pattern of n+1 lines ( 0 to n ): line i (i = 0 to n) has i stars ("*"), followed by (n-i) stripes ("-")

For example, printPattern(3) prints:

--- *-- **- *** 

hint: use a private recursive helper function, with more parameters, that does the work, e.g.:

 private void printPattern(int stars, int stripes) 

You may need another helper function...

int convertNum(int[] num)

Precondition: num.length > 0, and num contains digits between 0 and 9 (inclusive) Postcondition: return int representation of num

For example

 int[] num123 = {1,2,3}; convertNum(num123) returns 123 

hint: use a private recursive helper function, with more parameters, that does the work, e.g.:

 private int convertNum(int[] num, int atIndex, int lastIndex, int result) 

Note: Your helper method signature may not match this, it is offered only as an example.

ArrayList intersection( ArrayList AL1, ArrayList AL2)

Precondition: AL1 and AL2 are not empty, and elements in AL1 are unique, and elements in AL2 are unique, (but AL1 and AL2 can contain the same elements) Postcondition: return an ArrayList with elements that are in both AL1 and AL2, *** in the order they occur in AL1 ***, and *** leave AL1 and AL2 unchanged ***

For example:

 ArrayList AL1 = new ArrayList(); ArrayList AL2 = new ArrayList(); AL1.add("a"); AL1.add("b"); AL1.add("c"); AL2.add("b"); AL2.add("c"); AL2.add("d"); AL2.add("e"); ArrayList intersect = A3.intersection(AL1,AL2); System.out.println(AL1 + " intersect " + AL2 + " = " + intersect); prints: [a, b, c] intersect [b, c, d, e] = [b, c]