Main and Control Flow • Programming without ObjectEditor • Main Class • Control Flow •“Real” Programming •Linear •Branching •Looping • Programmer-Defined Overloading • Console Input
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Main and Control Flow
• Programming without ObjectEditor
• Main Class
• Control Flow
•“Real” Programming
•Linear
•Branching
•Looping
• Programmer-Defined Overloading
• Console Input
• Programmer-Defined Library Class
Programming Vs Bicycle Riding
Statements Expressions
Primitive Types
Least Privilege Interfaces Reuse Stepwise-
Refinement
Interface
Implements
Class
Method
Return Type/ Formal Parameter
Statement
Starting with the Big Picture
Variable (State)
Local Variable
Method Header
Signature
Name
Named Constant
Statement List
Statement ...
Statement
Starting with the Small Picture
Class
Method
Return Type/ Formal Parameter
Statement List
Statement ...
Variable (State)
Local Variable
Interface
Method Header
Signature
Name
Named Constant
Implements
Statement
Interface
Implements
Class
Method
Return Type/ Formal Parameter
Statement
Starting with the Abstractions
Variable (State)
Local Variable
Method Header
Signature
Name
Named Constant
Statement List
Statement ...
Statement
Data Abstraction
exports
Operation Abstraction
exports
Interface
Implements
Class
Method
Return Type/ Formal Parameter
Statement
Starting with Optional Components
Variable (State)
Local Variable
Method Header
Signature
Name
Named Constant
Statement List
Statement ...
Statement
Real-Work
Required
Focussing on Control Flow (“Real Programming”)
StatementStatement List
Statement ...
Statement List
Statement ...
Statement
Linear
Statement List
Stmt
Statement
Stmt
BranchingStatement List
Stmt
Statement
Stmt
Looping
Removing Training WheelsText Editor
ALoanPair Source Code
creates
Java Compiler
reads
ALoanPairObject (Byte) Code
creates
Java Interpreter
ALoanPair Instance
getTotalLoan()
instantiates
calls
ObjectEditor
main
calls
, Main Class
Main ClassObject (Byte) Code
Static method
Equivalent User Interfaces
Algorithm (edit)
Algorithm (edited)
Algorithm (soln)
• Create ALoanPair instance based on the two values entered by the user in the console window.
• Print the properties of the loan pair object in the console window.
• Pause until user presses some keystroke.
public static void main (String[] args) {
LoanPair loanPair = new ALoanPair(readCarLoan(), readHouseLoan());
print (loanPair);
pause();
}
Main Method
Method chaining
List of user-supplied argumentsmain header
public static void main (String[] args) {
Loan carLoan = readCarLoan();
Loan houseLoan = readHouseLoan();
LoanPair loanPair = new ALoanPair(carLoan, houseLoan());
print (loanPair);
pause();
}
Main Method without Method Chaining
Undefined
Stepwise refinement
readCarLoan()
readCarLoan()
• Prompt user
• Return an instance of ALoan constructed from the principal.
public static Loan readCarLoan() {System.out.println("Please enter car principal:");return new ALoan(readInt());
}
Called by class method (main)
Undefined
static DataInputStream dataIn = new DataInputStream (System.in); public static int readInt() {
try {return Integer.parseInt(dataIn.readLine());
} catch (Exception e) {System.out.println(e);return 0;
}}
readInt()• Wait for the user to enter a string (of digits) on the next line.
• Return the int represented by the string.
• In case the user makes an error or terminates input before entring a valid int, return 0 and print an error message.
try {return Integer.parseInt(dataIn.readLine());
} catch (Exception e) {
System.out.println(e);return 0;
}
Try-Catch Block
Exception Object
Program fragment that can cause exception
Exception Handler
public class ALoanPairDriver {
...
…
}
import java.io.DataInputStream;
public class ALoanPairDriver {
….
…...
}
Importing a Package
new DataInputStream(System.in)
new java.io.DataInputStream(System.in)
package java.io;
public class DataInputStream {
….
}
short name
full name
Import Declaration
Printing a LoanPair
Printing a LoanPair
public static void print (LoanPair loanPair) {System.out.println("****Car Loan*****");print(loanPair.getCarLoan());System.out.println("****House Loan****");print(loanPair.getHouseLoan());System.out.println("****Total Loan****");print (loanPair.getTotalLoan());
}
public static void print (Loan loan) { System.out.println("Principal:" + loan.getPrincipal()); System.out.println("Yearly Interest:" + loan.getYearlyInterest()); System.out.println("Monthly Interest:" + loan.getMonthlyInterest());}
Programmer-defined Overloading
public static void pause() {try {
System.in.read();} catch (Exception e) {
System.out.println(e);}
}
pause()Returns single char
System.out.println(pause());
Legal Expression & Statement
public static void pause() {try {
System.in.read();} catch (Exception e) {
System.out.println(e);}
}
Expression Vs Statement
System.out.println(pause());
5 + 3;
Illegal
Function Calls
• Can be used as expression
• Can be used as statement– When return value is to be ignored– Rarely happens– Check program to see all return values being
used as expressions
• Other expressions not statements
• Procedure calls never expressions
Multi-level Algorithm/Code
main
print (Loan)
readCarLoan readHouseLoan print(LoanPair) pause
readInt
Class-Level Decomposition
Monolithic Main Class(Loan User Interface and Loan Computation)
Object EditorProgrammer-defined Class(A Loan Pair)
Driver(ALoanPairDriver)
Class-Level Decomposition
main
print (Loan)
readCarLoan readHouseLoan print(LoanPair) pause
readInt
Separate Class
pause()readInt()
readDouble()
readBoolean()
readChar()
Keyboard
readString()
Using Keyboard
public static Loan readCarLoan() {System.out.println("Please enter car principal:");return new ALoan(readInt());
}return new ALoan(Keyboard.readInt());
Separation of Concerns
• Make independent piece of code as separate method.
• Make independent set of methods as separate class.
• Use operation and data abstraction!
Running Main
Single-Stepping
Step Into Vs Step Over
Inspecting Variables
Conditionals
printPassFailStatus(95)
printPassFailStatus(25)
public static void printPassFailStatus(int score) {if (score < PASS_CUTOFF)
System.out.println("FAILED");else
System.out.println("PASSED");}
PASS
FAIL
If-else Statement
if (<bool expr>)<statement 1>
else<statement 2>
If-Else Statement
<bool expr>true false
<statement 1> <statement 2>
Compound Statementpublic void fancyPrintGrade(int score) {
if (score < PASS_CUTOFF) {
System.out.println("**************");System.out.println("FAILED");System.out.println("**************");
}else {
System.out.println("**************");System.out.println("PASSED");System.out.println("Congratulations!");System.out.println("**************");
} }
Avoding Code Duplication in If-Else
public void fancyPrintGrade(int score) { System.out.println("**************");
if (score < PASS_CUTOFF) System.out.println("FAILED");
else {System.out.println("PASSED");System.out.println("Congratulations!");
}System.out.println("**************");
}
Avoding Code Duplication in If-Else
public void fancyPrintGrade(int score) { System.out.println("**************");
if (score < PASS_CUTOFF) System.out.println("FAILED");
else {System.out.println("PASSED");System.out.println("Congratulations!");
}System.out.println("**************");
}
If Statement
if (score == MAX_SCORE) System.out.println ("Perfect Score! Congratulations!");
if (<bool expr>) <statement>;
if Statement
<bool expr>true
false<statement>
Nested if-elsepublic static char toLetterGrade (int score) {
if (score >= A_CUTOFF) return 'A';else if (score >= B_CUTOFF) return 'B';else if (score >= C_CUTOFF) return 'C';else if (score >= D_CUTOFF) return 'D';else return 'F';
}
Nested If-Elseif (score >= A_CUTOFF) return 'A';else
if (score >= B_CUTOFF) return 'B';else
if (score >= C_CUTOFF) return 'C';
else if (score >= D_CUTOFF) return 'D'; else
return 'F';
Nested If-Else
Looping
printHello(2)
hello
hello
printHello(3)
hello
hello
hello
Loops
int counter = 0;if (counter < n) { counter = counter + 1; System.out.println (“hello”);}
public static void printHello(int n) {
}
Loops
int counter = 0;while (counter < n) { counter = counter + 1; System.out.println (“hello”);}
public static void printHello(int n) {
}
If Vs While Statement
if (<bool expr>) <statement>;
while (<bool expr>) <statement>;
if Statement
<bool expr>true
false<statement>
while Statement
<bool expr>true
false<statement>
while loop
<bool expr>
true
false
<statement >
Sentinel-based Folding
Adding Fixed Number of Loans
Loan loan1 = readLoan();Loan loan2 = readLoan();Loan loan3 = readLoan();Loan loan4 = readLoan();Loan sumLoan = ALoan.add(loan1, ALoan.add(loan2,
ALoan.add(loan3, loan4)));print (sumLoan);
Generalizing to Variable # Loans
Loan loan1 = readLoan();Loan loan2 = readLoan();Loan loan3 = readLoan();Loan loan4 = readLoan();…Loan loanN = readLoan();Loan sumLoan = ALoan.add(loan1, ALoan.add(loan2,
ALoan.add(loan3, Aloan.add(loan4, ……(add (loanN-1, loanN)*;print (sumLoan);
Loops + Arrays
Recursion
Variable # of Statements
Variable # of Subexpressions (function calls)
Space Efficient Adding of Fixed Number of Loans
Loan loan1 = readLoan();Loan loan2 = readLoan();Loan sumLoan = ALoan.add(loan1, loan2);loan1 = readLoan(); // 3rd loansumLoan = ALoan.add(sumLoan, loan1);loan1 = readLoan(); // 4th loansumLoan = ALoan.add(sumLoan, loan1);print (sumLoan);
More Space Efficient Adding of Fixed Number of Loans
Loan sumLoan = readLoan(); //first loanLoan nextLoan = readLoan(); //second loansumLoan = Aloan.add(nextLoan, sumLoan);nextLoan = readLoan(); // 3rd loansumLoan = ALoan.add(sumLoan, nextLoan);nextLoan = readLoan(); // 4th loansumLoan = ALoan.add(sumLoan, nextLoan);print (sumLoan);
More Space Efficient Adding of Variable Number of Loans
Loan sumLoan = readLoan(); //first loanLoan nextLoan = readLoan(); //second loansumLoan = Aloan.add(nextLoan, sumLoan);nextLoan = readLoan(); // 3rd loansumLoan = ALoan.add(sumLoan, nextLoan);nextLoan = readLoan(); // 4th loan
sumLoan = ALoan.add(sumLoan, nextLoan); nextLoan = readLoan(); //Nth loan sumLoan = ALoan.add(sumLoan, nextLoan); nextLoan = readLoan(); //sentinel
print (sumLoan);
N-1 repetitions
While Loop
Loan sumLoan = readLoan(); //first loan Loan nextLoan = readLoan(); //second loan while (nextLoan().getPrincipal() >= 0) {
sumLoan = ALoan.add(nextLoan, sumLoan);nextLoan = readLoan(); // next loan or sentinel
} print (sumLoan);
-1
Input Result
Program waits for ever for second loan
Boundary Condition
Loan sumLoan = new ALoan(0); //initial value Loan nextLoan = readLoan(); //second loan while (nextLoan().getPrincipal() >= 0) {
sumLoan = ALoan.add(nextLoan, sumLoan);nextLoan = readLoan(); // next loan or sentinel
} print (sumLoan);
Correct Solution
ALoan.add(new ALoan(0), add(loan1, add (…., loanN)
identity
Loan sumLoan = new ALoan(0); //initial value Loan nextLoan = readLoan(); //second loan while (nextLoan().getPrincipal() >= 0) {
sumLoan = ALoan.add(nextLoan, sumLoan);nextLoan = readLoan(); // next loan or sentinel
} print (sumLoan);
A Single Sentinel Value
Loan sumLoan = new ALoan(0); //initial value Loan nextLoan = readLoan(); //second loan while (nextLoan().getPrincipal() >= 0) {
sumLoan = Aloan.add(nextLoan, sumLoan);nextLoan = readLoan(); // next loan or sentinel
} print (sumLoan);
A Single Loan
Loan sumLoan = new ALoan(0); //initial value Loan nextLoan = readLoan(); //second loan while (nextLoan().getPrincipal() >= 0) {
sumLoan = Aloan.add(nextLoan, sumLoan);nextLoan = readLoan(); // next loan or sentinel
} print (sumLoan);
Two Loans
Multiplying Numbers (edit)
???
Multiplying Numbers (edited)
???
Multiplying Numbers int product = 1; int num = Keyboard.readInt(); while (num >= 0) { product = product*num; num = Keyboard.readInt(); }
print (product);
1*20*2*3
Identity
Comparing Two Solutions int product = 1; int num = Keyboard.readInt(); while (num >= 0) { product = product*num; num = Keyboard.readInt(); }
print (product);
Loan sumLoan = new ALoan(0); Loan nextLoan = readLoan(); while (nextLoan().getPrincipal() >= 0) {
sumLoan = ALoan.add(nextLoan, sumLoan); nextLoan = readLoan();
} print (sumLoan); // print value
Identityresult
nextVal
read first value
read other values
Binary folding function
!isSentinel(nextVal)
Generalized Folding of a Sentinal-Terminated List
a1
f
f
f
ana3a2
f: T, T T
F(x, I) x
T result = I;T nextValue = getNextValue()while (!isSentinel(nextValue)) { result = f(result, nextValue); nextValue = getNextValue(..);}
Generalized Folding SolutionLoan, int new ALoan(0), 1
ALoan.add(), *
>= 0
Comparing Two Solutions (Comments)
int product = 1; //identity int num = Keyboard.readInt(); // read next list value while (num >= 0) { // sentinel checking product = product*num; // binary folding function num = Keyboard.readInt(); // read next value }
print (product);// print value
Loan sumLoan = new ALoan(0); //identity Loan nextLoan = readLoan(); // read next list value while (nextLoan().getPrincipal() >= 0) {// sentinel checking
sumLoan = Aloan.add(nextLoan, sumLoan); // binary folding functionnextLoan = readLoan(); // read next list value
} print (sumLoan); // print value
Related Documents
