Practice with Functions and Strings
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Algorithmic Thinking and Problem Solving
But First: More About Functions
But First: How Are You?
Java Method Overloading
I told you that functions couldn’t have the same name.
I lied.
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Java Method Overloading
Java uses both the function name and the the list of arguments and types to determine which function to call.
Together they are called the function signature.
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Does the function have the right name?
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Does the function take the right arguments in the right order?
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Java will also try to convert types to find a match as long as no loss of precision occurs
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Function Input Validation
A common function design pattern is to check your inputs at the top.
Think about all the bad inputs you could possibly get from the caller.
int sum(int[] numbers) {
// check numbers to make sure it's sane
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null Arrays
What is the value of array declared below?
int[] output = null;
System.out.println(output);-
Java has a special value that can be used to indicate that an object has not been initialized:
null. -
nullis not a valid object: it has no properties or methods that you can use. -
Attempts to use
nullwill result in an error
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Defensive Programming 101
Always check objects for null.
Java and other Java-like languages now also have better primitives for dealing
with null and avoiding
the Billion Dollar
Mistake.
Casting
If you want to force Java to convert a variable from one type to another you can try applying a cast.
int i = 10;
double d = i; // This works since no information is lost
i = d; // This does not work since we'd have to throw out the fraction
i = (int) d; // But we can force Java to do it> Click or hit Control-Enter to run the code above
Let’s Solve Some Problems!
String Reverse
Given a String, return it in reverse order.
First, what is our algorithm? I can think of at least three ways to do this…
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Examine each character in the input
String -
Put it in the right place in the output
String
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Preparing for CBTF Quizzes
Our quizzes get more challenging from this point forward. Here’s how to prepare.
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Review the lecture slides
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Go over the HW125 practice problems
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Go over the HW125 practice problems
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Go over the HW125 practice problems
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Go over the HW125 practice problems
Preparing for CBTF Quizzes
int earnGradeOnQuiz() {
int currentGrade = 0;
currentGrade += reviewSlides();
while (workOnHomeworkProblems()) {
currentGrade++;
}
return currentGrade;
}Dropped Grade Policy
CS 125 has a generous dropped grade policy. However, these are not "get out of class free" cards.
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Dropped lectures and labs are pre-excused absences intended to accommodate all the reasons you might miss class or not complete a homework problem: sickness, family emergencies, travel, religious obligations, extracurricular activities, etc.
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As a result we don’t excuse absences. Please don’t email us about this.
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We expect you to try to attend and complete everything. But the dropped grades are for times when circumstances intervene.
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If you use them up skipping class just because you don’t feel like coming, and then your fish dies and you are bereft, you don’t get more.
Announcements
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MP0 is out and due next weekend. The early deadline is this weekend on your deadline day. Please get started! Office hours start immediately after class in Siebel 0403.
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My office hours today will be in Siebel 0403 from 1–3PM.