Strings

Strings
> Click or hit Control-Enter to run the code above

So far we know how to store a few different types of data using Java’s 8 primitive types:

Integers: byte, short, int, long
Floating point numbers: float, double
Character: char
True or false: boolean

Much of the interesting data in our human world is in text form.

As a computer scientist, you call text a string.

(I realize that I cannot remember not knowing that term. I guess I’m old, or just have really become a computer scientist.)

Unsurprisingly, Java has a String type.

We can declare, assign, and pass them to functions like primitive types.

String maybe;
maybe = "Challen"; // No, bad
maybe = "Geoff"; // Better, thanks
callMe(maybe); // You have my number?

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In Java a String is our first 1 example of an object.

Objects combine state (like variables) and behavior (like functions).

Each String has state: the array of characters in that string
Each String also has behavior: functions that we can call on it that operate on its state

Primitives:

Store something that can be represented as a single number
Have type names that start with a lowercase letter: int, char, etc.

Objects:

Can be made up of multiple other objects or primitive types
Have type names that start with an uppercase letter: String

You will get a lot of practice working with and designing your own objects.

For now we’re going to use strings as a gentle introduction to using objects.

Normally to initialize an object in Java you use the new keyword.

String myString = new String("ABC");
String anotherString = new String("DEF");

However, strings are so common that Java provides a shorthand:

String myString = "ABC";
String anotherString = "DEF";

(In practice there are minor differences between the two code snippets above, but we’re not going to worry about them.)

In Java, the String object is so important that is (almost 2) the only object in Java that supports literals.

int first = 3; // 3 is a numeric literal
boolean isHot = true; // true is a boolean literal

char one = 'a'; // one is a char literal
String test = "Test Me"; // "Test Me" is a String literal

Do you remember? We’ve seen new before…

int[] array = new int[8];

Java arrays are also objects—which is why we create them with new and can access their length property as array.length.

We can combine strings using the concatenation operator: +.

String first = "Geoffrey";
String last = "Challen";
String full = first + " " + last;

> Click or hit Control-Enter to run the code above

We access an object’s state and methods using dot notation.

String example = "test";
System.out.println(example.length());
System.out.println(example.replace('t', 'b'));
System.out.println(example.toUpperCase());

> Click or hit Control-Enter to run the code above

> Click or hit Control-Enter to run the code above

Given an array of chars a String, find all cases where consecutive characters are the same.

First, what is our algorithm?

Examine each character in the string
Compare it with the next value—but how do we get at that?
Print it out if they are the same

> Click or hit Control-Enter to run the code above

Given a phone number formatted like "111.222.3333", convert it to "(111) 222-3333".

First, what is our algorithm?

Divide the input at each "."
Combine the values appropriately to create the new string

> Click or hit Control-Enter to run the code above

Our quizzes get more challenging from this point forward. Here’s how to prepare.

Review the lecture slides
Go over the HW125 practice problems
Go over the HW125 practice problems
Go over the HW125 practice problems
Go over the HW125 practice problems

int earnGradeOnQuiz() {
  int currentGrade = 0;
  currentGrade += reviewSlides();

  while (workOnHomeworkProblems()) {
    currentGrade++;
  }

  return currentGrade;
}

MP0 is out and due next Monday. Please get started!
Quiz 2 has been rescheduled to extend through tomorrow. Please sign up to take it!
No course activities today because it’s cold!
But homework continues and staff are available for help on the forum.
Please fill out the initial student survey. 1% extra credit for anyone who does by Sunday 02/03/2019.

Storing Data

What’s Missing?

Strings

Java Strings

Strings Seem Familiar, But Behave Differently

Our First Object

What does it store, and what does it do?

Objects v. Primitives

Objects

Strings

String Literal

Arrays Are Also Objects

Combining Strings

Creating Strings

Dot Notation

Dot Notation

Fun With Strings

Questions About Strings?

Consecutive Identical Values

String Manipulation

Preparing for CBTF Quizzes

Preparing for CBTF Quizzes

Announcements