Description
Exercise 1 • Write the complete Java program • Use the two methods • Main method: • Main gets 3 numbers from the user • Invokes the problem solving method with those 3 numbers • Gets the average back • Problem solving method: • Receives 3 numbers • Computes the average • Returns average Exercise 2 /* Lab 3, Exercise 1. */ class Average { // the main method contains all interac=ons with the user public sta=c void main (String[] args) { // Declare Variables double n1, n2, n3; // numbers to averages double average; // the averagage // prompt the user to enter 3 numbers System.out.print( “Enter three numbers: ” ); n1 = ITI1120.neadDouble(); // read first number n2 = ITI1120.readDouble(); // read second number n3 = ITI1120.readDouble(); // read third numre // call problem solving method double result = average( n1, n2, n3 ); // display maximum value System.out.println( “The maximum is: ” + result ); } public sta=c void averagedouble num1, double num2,double num3) { // Declare variables double sum; // sum of the numbers double avg; // RESULT: average of the numbers // BODY sum = num1 + num2 + num3 ; avg = sum / 3; // RETURN RESULTS return(avg); } } Program Memory Terminal/Output Screen n1 n2 n3 average Working Memory num1 num2 num3 sum avg 7 Using the Debugger • Using Dr. Java’s “debug mode”, you can trace your Java program as it runs. – You can go through the program one step at a time. – You can stop the program at “break points” of your choosing. – You can check the values of variables. • Try this for the program you wrote for Exercise 1, the average of 3 numbers. • Use the programming mode to follow the execution of the program. 8 Break Points • Select a line of your program, and under the debug menu, choose “toggle break point on this line”. – The first System.out.println statement is a good choice – This will change the colour of the chosen line of code to red. • You can also right-click on a line and select “Toggle BreakPoint”. – Many lines can be (de)selected this way. • When you run the program, the program will stop just before this line is going to be executed. • In the interactions window, the debugger will tell you where the program is, and the current line of code will be coloured light blue. 9 Watches • To keep track of the values of variables as they change, use a “watch” – Double-click on an empty area in the “ name ” column, then type in the name of a variable, and hit ‘enter’. – If the variable already has a value, it will be shown. If the variable does not yet have a value, the value will say . • Try this for all of the variables you use in your program for example 1. • As the program executes, each time the program stops in the debugger, the current values of the variables will be shown. 10 Controlling Execution • With the debugger, there are four ways to advance through a program • Resume – The program will run up to the next break point, or the end of the program if there are no more break points. • Step into – Use this for the most detailed debugging – The program will move to the next statement – even if that statement is in another method. – This will not go into methods in the Java software development kit. 11 Controlling Execution • Step over – Most commonly used – Use this to move to the next statement in the current method. – If the current line of the program calls one or more methods, all of those methods will be invoked, and returned from. • Step out – Often used when you have stepped into a method and you want to go back quickly to the previous method. – Use this to run as far as the end of the current method. • Try using “Step over” to go through your Exercise 1 program one statement at a time. • But use “Step into” when you arrive at the call of the problem solving method (computeAverage). 12 Exercise 3 Write a complete Java program that asks a user for temperature in Fahrenheit and converts it to Celsuis. Your program should have 1. the main method that communicates with the user 2. and a method caled calculateCelsuis that converts temperature expressed in Fahrenheit to Celsius, according to the following formula: C ← ( F – 32) * 5 / 9 and returns the computed value to the main. 13 Exercise 4 Write a complete Java program that given a two digit positive integer prints that number in reverse. – For example: Your program will transform the two digit integer 12 into 21 (and print 21). • Hints: – The first digit is the result of dividing the integer by 10 (integer division) – The second digit is the remainder of the division by 10 • e.g.:original integer: 12 – first digit is 12 / 10 = 1 – second digit is 12 % 10 = 2 • Use two methods model – as you did in Exercise 3). • Complie and Test your program 14 Built-in math functions • The Math class – Automatically loaded: no import required. • Math.abs() – absolute value | x | • Math.pow() – exponentiation • Math.sqrt() – square root √ x • Examples – Math.abs(-3) Result: 3 | -3 | = 3 – Math.pow(2,5)Result: 32.0 25 = 32 – Math.sqrt(49)Result: 7.0 √ 49 = 7 • See other math functions in Section 5.9 of the textbook • On line description at http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Math.html 15 Exercise 5 • Consider the following problem: Given coordinates of 2 points in the plane (xa,ya) and (xb, yb), compute the distance between the two points, according to the following formula: Write a complete Java program for the above problem. (Use two methods – as you did in Exercises 3 and 4). Compile and test your code. (xa − xb) 2 +(ya − yb) 2 16 Note • According to standard convention, the class names in Java start with Upper-case and names for variables and methods start with lower case. • Use indentation to make your programs readable – HINT: in Dr Java, if you type Cntrl-A (all your code will be selected) and then type Tab, Dr Java will organize your code using standard indentation convention.
