Strings and Chars

Question 1

What are Strings?

Answer 1

A data type used for storing text; a collection of characters that maintain their order

Question 2

What characters are valid in a string?

Answer 2

All characters are valid, but to get certain characters you must use escape sequences (eg \n)

Question 3

What are the escape sequences?

Answer 3

”: "
:
new line: \n
tab: \n
and more

Question 4

In Java, what types can be turned into a String?

Answer 4

All types

Question 5

What is concatenation?

Answer 5

Adding up strings to make a longer string using the + or += symbols

Question 6

How does the compiler decide when to do addition or concatenation?

Answer 6

The operation a + b only means addition if both a and b are numbers of some kind. Otherwise, if the other side is not a String, it is converted to one

Question 7

What are objects?

Answer 7

Data types that begin with a capital letter; larger chunks of data made up of the primitive data types

Question 8

What is stored on the stack when you use objects? Why?

Answer 8

A reference to the data’s location on the heap. At compile-time, the computer doesn’t know how much space an object will need.

Question 9

What is the function in processing that lets you draw text on the canvas?

Answer 9

text(String, x, y);
(draws a string with its lower left corner at (x, y). Characters are mostly above the y value, but characters with descenders will go lower.)

Question 10

What are the other text functions in processing?

Answer 10

textSize(p): sets the size of the text, in pixels
fill(): controls the text colour
textWidth(String): how many pixels wide will it be (based on textSize)
textAscent(): how many pixels “above the line”
textDescent(): how many pixels “below the line”

Question 11

How can you get user input in your processing programs?

Answer 11

Using JOption Pane.
Add import javax.swing.JOptionPane; at the very top of your program, and use JOptionPane.showInputDialog(“prompt”) to get a String from the user

Question 12

How can you turn something else into a String?

Answer 12

use str(x) (this is done automatically for functions that have strings as arguments)

Question 13

How can you change a String containing characters that form a valid int or float literal, how can you obtain an actual int or float?

Answer 13

int() and float() ((int)string and (float)string don’t work)

Question 14

What happens if you try to convert a string that is not a valid number into a number data type?

Answer 14

it will print NaN

Question 15

Describe the structure of a string

Answer 15

A string is made up of a number of characters. Each character has a specified “index” (box or slot). The index of the first character in the String is 0

Question 16

How should you compare strings? Why?

Answer 16

You can’t use == on Strings because they are objects, not a primitive data type, so you would just be checking if the memory addresses are the same. Instead you should use string.equals(String) or string.equalsIgnoreCase(String)

Question 17

How can you find out the length of a String?

Answer 17

string.length();

Question 18

How can you find a character at a specific index in a String?

Answer 18

string.charAt(int)

Question 19

What is the char type?

Answer 19

used to hold one single character; a primitive type (traditionally 1 byte, but occupies 2 bytes in Processing)

Question 20

Is there a difference between how you must write char literals and String literals?

Answer 20

‘x’ is a char, “x” is a String

Question 21

What must you write to get ‘ as a char?

Answer 21

’'’

Question 22

Why can you convert back and forth between a char and an int?

Answer 22

A char is simply an integer underneath (ASCII or UNICODE), and it is smaller than any other numeric type, so you can do an implicit cast from char to int.

Question 23

What are the built-in functions to check for specific kinds of characters?

Answer 23

boolean Character.isLetter(char c);
boolean Character.isUpperCase(char c);
boolean Character.isLowerCase(char c);
boolean Character.isDigit(char c);

Question 24

How can you convert from a character to a string?

Answer 24

the str() command

Question 25

What is the built-in key variable?

Answer 25

a char that tells us which key is being pressed