Conditionals

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From the course by Duke University

Java Programming: Solving Problems with Software

2500 ratings

Duke University

Java Programming: Solving Problems with Software

2500 ratings

Course 1 of 4 in the Specialization Object Oriented Programming in Java

Learn to code in Java and improve your programming and problem-solving skills. You will learn to design algorithms as well as develop and debug programs. Using custom open-source classes, you will write programs that access and transform images, websites, and other types of data. At the end of the course you will build a program that determines the popularity of different baby names in the US over time by analyzing comma separated value (CSV) files. After completing this course you will be able to: 1. Edit, compile, and run a Java program; 2. Use conditionals and loops in a Java program; 3. Use Java API documentation in writing programs. 4. Debug a Java program using the scientific method; 5. Write a Java method to solve a specific problem; 6. Develop a set of test cases as part of developing a program; 7. Create a class with multiple methods that work together to solve a problem; and 8. Use divide-and-conquer design techniques for a program that uses multiple methods.

From the lesson

Fundamental Java Syntax and Semantics

In this module, you will learn to write and run your first Java programs, including one program that prints “Hello!” in various countries’ languages and another where you will analyze the perimeters and other information of shapes. To accomplish these tasks, you will learn the basics of Java syntax and how to design stepwise solutions with programs. By the end of this module, you will be able to: (1) Download and run BlueJ, the Java programming environment for this course; (2) Access the documentation for the Java libraries specially designed for this course; (3) Edit, compile, and run a Java program; (4) Construct methods, variables, if else statements, and for each loops in Java; and (5) Use Iterables (like DirectoryResource) to run a program that iterates over multiples lines in a document or webpage or multiple files in a directory.

Conditionals3:25

Meet the Instructors

Owen Astrachan
Professor of the Practice
Computer Science
Robert Duvall
Lecturer
Computer Science
Andrew D. Hilton
Associate Professor of the Practice
Electrical and Computer Engineering
Susan H. Rodger
Professor of the Practice
Computer Science

Now, let's see how to execute code with conditional statements in it.

Here we have a function f, which has some if and if, else statements.

We have another function g.

We'll assume we've used BlueJ's interface to invoke the method or

function g to start with.

The first statement declares a variable a.

So we'll make a box for a.

Even though this statement initializes a,

it's going to take us several steps to compute that value.

So we're going to leave a's value as 0,

until we compute the value of the method f, applied to arguments 3 and 4.

To evaluate this called to f, we make a frame,

passing the values of the parameters.

Note where to return and then we move the execution arrow to the first line f.

The next line of code is an if statement,

whose conditional expression is x less than y.

We evaluate that expression and find 3 less than 4 is true.

So I move the execution arrow into the then clause of this if statement and

continue executing.

The next statement is a call to System.out.println which is how you print

something in Java.

We write x less than y in our output and then, we return y plus x.

This values follows the same rules you've already learned for return statements.

We evaluate the expression to get the return value which is 7.

Which is then what the function call evaluates to and

will return back to the caller, destroying the frame for f.

Now we're ready to finish initializing a,

since we know that the call to the method f evaluated to 7.

So, a is now 7.

Now, we're ready for the next line of code in g.

We make a box for b.

And we call f passing in the arguments 7 and 5.

Once again, we want to evaluate the condition x less than y.

However, now x is 7 and y is 5.

So x less than y is false.

We find the closed curly brace for this if statement and

see that the if statement has an else clause.

So we move the execution arrow into the start of the else clause and

continue executing from there.

First, we see the System.out.println statement and

this prints the line x is greater than or equal to y.

Then we reach another if statement.

This if statement is nested inside of the else but

that doesn't affect the rules of how we evaluate it.

We see that the conditional expression is false since 7 is not greater than or

equal to 8.

There's no else clause, so we move the execution arrow

immediately past the closed curly brace and continue execution.

There are not anymore statements inside the else clause.

So remove the execution arrow outside of the else clause and keep going.

Next, we have a return statement.

So we evaluate the expression x minus 2 to find that the return value is 5.

This then gets returned to the place we noted.

So we destroy the frame for f and return back to g.

We finished the assignment statement and now we're ready for

the return statement from g.

We execute that and we're done with method g.

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