Exam 2 Topics
CS141: Introduction to Programming, Fall 2011

General Comments and Recommendations

• The exam will cover Nested Loops in Chapter 4 (sec 6) and Chapters 5-6 of the text. Note that the material is cumulative so you are still expected to remember the earlier material.
• The exam will be 1 hour long. It will be closed book. Electronic devices, of any kind, will not be allowed.
• It is strongly recommended that students:
  • Re-read the text
  • Do the self-check exercises in each chapter (answers are in the text)
  • Review the reading quizzes
  • Review the programming code-completion and programming exercises.
  • Be able to do the Nested-loop problems in exercise.
  • Be able to do the Method problems in exercise.
  • Be able to do the Array problems in exercise.

Code from Class

Here is the code that we created in class on Monday (Nov 14):

• Sec 1: Practice1.java
• Sec 2: Practice1.java and Practice2.java

Chapter 4.6: Nested Loops

• You should be able to do these problems.
• Nested loops are often needed to work with 2D arrays.

Chapter 5: Methods

• What is a method?
• Why do we have methods?
  • Organization, Modularization and Reusability, Efficiency
• Anatomy of a Method Declaration:
  • method name
  • parameters (type & name for each)
  • return type
  • body
• What does it mean "to call" a method.
• Example: Rolling dice - see in class problems.
• What is the scope of a variable?
  • See last problem of in class problems. Declaring variables local to a block of code.
• Recursion:
  • What is a recursive method?
  • What is the tyoical form: base case, and recursive case.
  • Know how to write a recursive method, e.g. that
    • prints out a list of numbers
    • computer the sum 1 + 2 + ...+ n
    • computes n! (i.e. n factorial)

Chapter 6: Arrays

• Declaring: int[] myNums; // creates only a reference!
• Initializing/Creating elements: // size is always fixed.
  • myNums = new int[10];
  • myNums = { 0,1,2,... };
• Setting the values:
  • Individual elements: myNums[3] = 255;
  • Using a loop to set entire arrays:
    • for (int i=0; i<myNums.length; i++) myNums[i] = 10;
    • using the fill method in the java.util.Arrays class: Arrays.fill(myNums,10);
• Copying arrays: Beware!
  • int[] myNums2 = myNums; // does not make a copy!!
  • use loop or Arrays.copyOf
• Enhanced loop: for (int element: myNums) sum = sum + element; // don't use to modify the array element values!
• Other: summing, searching, max/min, inserting elements, removing elements, sorting, etc
• Passing arrays as parameters in methods !!! Copy by reference vs Copy by value
• 2D Arrays
  • Declaring
  • Representation as an array of arrays
  • In methods: parameters and return values.
  • Higher dimensional arrays

Chapter 6: ArrayLists

• The ArrayList class - many methods: add, get, remove, size, isEmpty, toArray
• Benefits: can grow and shrink, Cons: takes up more space, may be slower than arrays but only an issue if size is really, really big.
• Creating an ArrayList
  • must import java.util.ArrayList
  • ArrayList<String> myList = new ArrayList<String>(); // creates an empty list
  • Can't use primitive types, must use Object representation of primitive (wrapper):
    ArrayList<int> myNums = new ArrayList<int>(); // NOT ALLOWED
    ArrayList<Integer> myNums = new ArrayList<Integer>(); // OK
• Setting the values of an ArrayList:
  • myList.add("hello"); // adds a single element to the end of the list
  • ArrayList myList = new ArrayList(Arrays.asList("hi","there","today")); // adds multiple elements all at once
• Accessing or Printing the values of an ArrayList:
• System.out.println("myList element is " + myList.toString() ) ; // prints out the list
• Print using a loop (for-loop or enhanced for-loop), e.g.

  for (String s: myList) {
  
     System.out.println(s); 
  
  }

• Beware - must be careful removing elements using a loop.