1. What/how do we care about a program?
Robustness
 Error Handling
Correctness
 Software Testing
Efficiency (speed, space)
 Algorithm Analysis
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2. Things that can go wrong
Logical error – The program is incorrect 
Environmental error - e.g. out of memory
I/O error – e.g., lost network connection.
Let’s handle it!!
Beyond programmer’s control
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3. Exceptions In Java, they are classes
Throwing Exceptions is Java’s way of telling you something has gone wrong
When an “exceptional condition” occurs, an exception object is created storing information about the nature of the exception (kind, where it occurred, etc.). When this happens, we say that “an exception is thrown”.
The JVM looks for a block of code to catch and handle the exception (do something with it)
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4. Exception throwing bad thing happens The sequence of throwing
exceptions
method c
 exception occurs X
If the exception cannot be handled here, it will continue to throw back
method b  method c()
method a  method b()
main() calls  method a()
JVM starts application at main()
The sequence of calling
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5. Try-Catch-Finally Blocks
program statements; some of which may throw an exception }
catch ( ExceptionType1 exception ) {
program statements to handle exceptions of type ExceptionType1
or any of its subclasses
catch ( ExceptionType2 exception ) {
program statements to handle exceptions of type ExceptionType2 …
other catch clauses
catch ( ExceptionTypeN exception ) {
program statements to handle exceptions of type ExceptionTypeN
finally {
this block is optional;
this block will execute whether or not an exception is thrown

6. try {
int i=1,j=2;
Exception myEx=null;
String s="0.2";
i=Integer.parseInt(s);
if (i > j)
throw new RuntimeException();
int[] A = new int[5];
i=1;
if (i<2 || i>4)
throw new IndexOutOfBoundsException();
i = 5;
i = A[i]; }
catch (ArithmeticException ex) {
System.out.println("\n"+ex.toString());
ex.printStackTrace();
catch (NullPointerException ex) {
System.out.println("I'm here 12345");
catch (NumberFormatException ex) {
System.out.println("\n"+ex.toString());
ex.printStackTrace(); }
catch (IllegalArgumentException ex) {
catch (ArrayIndexOutOfBoundsException ex) {
catch (IndexOutOfBoundsException ex) {
catch (RuntimeException ex) {
finally {
System.out.println("\nWe are done. Finally!!");
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7. String fname;
Scanner inS = null;
fname = (args.length != 0 ? args[0] : "/home/ADILSTU/ccli/Public/IT179/exps.txt");
try {
File file = new File(fname);
inS = new Scanner(file); }
catch (FileNotFoundException ex) {
System.out.println("Can't find file: "+fname);
System.exit(-1);
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8. Categories of exceptions
These categorization affect compile-time behavior only
Checked exceptions – descended from class Exception, but outside the hierarchy rooted at RuntimeException. The compiler will check that you either catch or re-throw checked exceptions.
Unchecked exceptions – (aka Runtime Exception ) represent the kinds of errors your program can avoid through careful programming and testing. The compile does not check to see that you handle these exceptions.
These represent some error, not programmer’s fault, but
the programmer can (should) do something about it
They are programmer’s fault, the compiler can’t
do a thing.
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9. Unchecked Exceptions handle:
Logical error – The program is incorrect 
Environmental error - e.g. out of memory
I/O error – e.g., lost network connection.
Checked Exceptions handle:
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10. Java’s Exception Hierarchy
Unchecked
Checked

11. Correctness  Software Testing
You should “test” throughout the software development cycle, namely, every stages:
After the analysis and design are completed
During the implementation (test driven development) (Write a little, test a little)
After the implementation is completed
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12. Efficiency (speed, space)
 Efficiency Analysis
An algorithm’s performance can be measured by:
Time complexity
Space complexity
How long it takes to execute.
How much additional space the algorithm needs. (memory, storage, tape).
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13. Time Complexity: Count Instructions
Statements
Cost 1
double average( int []a, int n ) { 2
double sum = 0; 3
int count = 0; 4
while ( count < n ) {
n + 1 5
sum += a[count]; n 6
count++; 7 } 8
if ( n > 0 ) 9
return sum / n; 10
else 11
return 0.0f; 12
TOTAL
3n + 5
How many times
will each instruction
execute?
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14. asymptotic approach  n2 n+(n-1)+(n-2)+......+3+2+1 = n(n+1)/2
for (int i=0; i< n; i++) {
for (int j=i; j < n; j++) { }
 n2
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15. Consider the worst part of the program
if (....) { }
else { n2
 n3 n3
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16. Big-O notation in Algorithm Analysis
for (int i=0; i< n; i++) { }
for (int j=0; j< n; j++) {
for (int k=0; k<n; k++) {
Big-O notation in Algorithm Analysis
 n
 n3
O(c+n+n3+n2)
 O(n3)
 n2
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17. Linear Search Statements Cost 1
int linearSearch( int [] a, int n, int target ) { 2
int i = 0; 3
while ( i < n ) {
n + 1 4
if ( target == a[i] ) n 5
return i; 6
i++; 7 } 8
return –1; 9
TOTAL
3n + 3
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18. O(n-s)=O(n) O(3) = O(1) // select the minimum between a[s] to the end
// and return the index of the minimum //
private int min(int a[], int s){
int m = s;
for (int i=s; i < a.length;i++) {
if (a[i] < a[m]) m=i; }
return m;
// exchange the contents of a[i] and a[j]
private void exchange(int[] a, int i, int j) {
int temp = a[i];
a[i] = a[j];
a[j] = temp;
O(n-s)=O(n)
where n is the size of the array
O(3) = O(1)
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19. public void sort(int a[]) {
// select right element for a[i]
for (int i = 0; i<a.length-1; i++) {
int j = min(a,i);
exchange(a,i,j); }
Selection Sort
(a quadratic sort)
O(n2) 9 6 3 4 2 8 5 2 6 3 4 9 8 5 2 3 6 4 9 8 5 2 3 4 6 9 8 5 2 3 4 5 9 8 6 2 3 4 5 6 8 9 i i j i j i i j i j j j
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20. Logarithm (binary search) Linear (sequential search)
n log n (quick sort)
Quadratic (n2, selection sort, insertion sort)
Polynomial (Primality test)
Nondeterministic polynomial (Traveling Salesman problem)
Exponential (en Backtracking)
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21. Big-Oh (): Linear Search
TlinearSearch(n) = 3n + 3 = (n) for c = 4 and n0 = 0,
in the worst case. n2
TlinearSearch(n) = (n2)
But this is an abuse of
O-notation 4n
3n + 3
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22. Some Common Computing Times
log2n n
n log2n n2 2n 1 2 4 8 16 3 24 64
256
65,536 5 32
160
1,024
4,294,967,296 6
384
4,096
1.84  1019 7
128
896
16,384
3.40  1038
2,048
1.16  1077 9
512
4,608
262,144
1.34  10154 10
10,240
1,048,576
1.80  10308
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