Java Levels 0-2 Flashcards
strings
“string”
must have quotation marks
String
integers
whole #’s w/ no decimal point
weird math
int
doubles/floating-point values
real numbers
numbers w/ decimal points
double
booleans
true/false (LOWER CASE)
boolean
operators
the symbols that we use to perform calculations on diff values
arithmetic operators
+ - * / %
parenthesis used same as in math
order of operations same
concatenation
if you “add” anything to a string, it will stick that value on to the string
“Hello” + “werld” = “Hellowerld”
50 + “8” = “508”
“Zoobah” + 0.5 * 3 = “Zoobah1.5”
integer division
when 2 integers r divided, the result is always an integer
will chop off decimal part NOT round
6/4 = 1
2 / 3 = 0
1 / 5.0 = 0.2 (if ether of the values is a double, will do normal division)
modulus division
only works on integers
gives the remainder of the first number divided by the second number
6 % 4 = 2
12 % 3 = 0
3 % 4 = 3 (if 1st # is less than 2nd #, answer is always 1st number)
variables
named containers for values
fundamental tool for programming
must be declared
variable declarations
statements, so must end in semicolons
int blah;
double aVariable;
String porty;
int ting, roo;
assignments/statements
putting a value into a variable for storage
=
blah = 10;
aVariable = 0.6;
porty = “Teapot”;
ting = 10 / 5;
roo = blah / ting; can use other variables in math expression and assignment statements
combining declarations & assignments
int abc = 12, def = 801;
double xyz = 10.5;
String ijk = “pointy hat”;
self assignments
can use a variable on the right hand side of its own assignment
int fumu = 10;
fumu = fumu + 3;
fumu = fumu - 5;
type mismatch
when variables r assigned values that don’t match their type
int abc = 10.0;
double def = 3; this works tho cuz Java can turn integers into doubles when necessary
name conflict
w/in a Java program, no 2 variables can be declared w/ the same name, even if they r dif types
int neato;
String neato;
import
brings in a class from Java’s class library, a large # of classes & methods written by the poeple who made Java, 2 help ppl use Java
javax.swing.JOptionPane
a collection of useful methods that can pop up diff windows 2 do stuff
showInputDialog
a method inside of JOptionPane
pops up a window tht lets the user type a string
will then assign the string tht was typed to the variable on the left side of the =
only works for Strings
Integer.parseInt
Double.parseDouble
takes any String in the parenthesis & tries to turn it itno an integer(or double)
condition
an expression that compares 2 values & gives a Boolean result(true/false)
5 > 12 (true)
3 > 7 (false)
6 >= 6 (true)
conditional operators
< less than
> greater than
<= less than/equal to
>= greater than/equal to
== equal to
!= not equal to
don’t work w/ strings
.equals()
bah.equals(wip) would give true if both bah & wip r the same string
if
if (a < b) {
System.out.println("blah");
}
if the condition inside the parenthesis is true, then Jaca will do the code inside the curly braces. otherwise, skips it.
else
if (a < b) {
System.out.println("blah");
} else {
a = a + 10;
}
The code inside the curly braces after the else keyword will be done if the condition turns out to be false
else if
if (a < b) {
a = a - 5;
} else if (b > c) {
b = b + 9;
}
If 1st condition is false but 2nd is ture, will do 2nd code.
If 1st is true, then will do 1st code & skip else if
if-else chains
You can put an if, lots of else ifs, and an else together in a “chain” of conditions
can have as many else ifs as u want, but only one if @ beginning and 1 else @ end
Java will work its way down the “chain” & do the code inside the curly braces for the 1st condition which is true
exclusive, so will only actually do the code b/w 1 set of curly braces
branching
refers to the ability of the program to do diff things under diff conditions
Boolean operators
&& and
|| or
! not
used only with conditions
boolean order of operations
AND always before ORs unless parenthesis
math operators ALWAYS take precedence over Boolean operators
(x - 5 < 2) will do x - 5 first
