Java Flashcards
java: to write a comment type
//
java: java filenames end with
.java
java: Java is a
compiled language
java: a compiled language is one that
must be converted from human readable code to computer readable code before running.
java: javac is short for
java compiler
java: To run a java file that you have already compiled you type
java Filename
java: To compile a java file and then run it, type
javac Filename.java double ampersand
java Filename
java: Variables in java require you to
specify their type
java: To create a string variable, type
String myString = “string”;
java: To print a string with a variable in it to the console, type
console.printf(“I’m %s”, “Alen”)
java: do not forget
to end lines with a semicolon
java: To accept a user input into the console into a variable, type
String myString = console.readLine(“string”);
java: a multi line comment is denoted with
/* */
java: Java’s variable types are
int
String
boolean
java: To write a conditional statement, type
if (10 == 10) {
}
java: The global object that controls the system is called
System
java: To make the system object exit, type
System.exit(0);
System: Any exit code other than 0 means
that the program exited abnormally.
System: an exit code of 0 means
that the program exited intentionally.
java: To convert a string to an int, type
Integer.parseInt(intString);
java: To return a boolean of whether a string variable is the same as another string, type
myString.equals(“string”);
java: To return a boolean of whether a string variable is the same as another string case insensitive, type
myString.equalsIgnoreCase(“string”);
java: the “or” character for conditional statements is
||
java: the “and” character for conditional statements is
double ampersand
java: To run some code before entering a while loop, type
do {
} while {
}
java: Variables declared inside the do while loop are
not available outside it
android: IDE stands for
integrated development environment
android: Software you can write android apps in is called
Android Studio
android: When creating an android project, the package name
is your unique identifier that differentiates you from other developers on the play store. Make it unique upfront.
android: When creating an android project, the project name
is the name you will see in the play store, so make it correct up front.
android: Gradle is
the build system that builds android apps
android: To run your android app on your computer
press play on the toolbar press "..." build an emulator Make sure to use an "armeable" version of android. and keep the rest defaults press play again in the toolbar again choose the emulator in the dropdown
android: to regenerate all of the files
click the menu option, “build” then “clean project” and then “rebuild project”
android: The minimum SDK is
the lowest version of android our app works on.
android: To view almost any section of Android Studio
click the square in the bottom left corner and click on it in the dropdown
android: The file main/res contains
all of the resources or static files of the app
android: The file main/res/layout contains
all of the screens/views
android: Build time errors appear in
the bottom toolbar option “messages”
android: Run time errors appear in
the bottom toolbar option “android”
android: To change a view visually instead of using code,
click the “design” tab
android: To set textSize to be size that is relative to the screen size, type
10sp
android: To make an element stretch to the outer edges or shrink to just fit it content
click the double arrows above the phone preview
android: It is better to change the id of an element in the
design tab instead of the xml tab because it automatically changes all references to that id as well, while the code does not
android: A view in android is
a page element
android: A relative layout is
the container page that holds the views
android: An easy way to get rid of the action bar is to
go to values/styles.xml and change the theme to one with no action bar
android: The meta information of an app like name, theme, icon are saved in
AndroidManifest.xml
java: To clear the java repl, type
:cls
java: To return a boolean of whether or not a substring is contained in a string, type
myString.contains(“string”);
java: To lower case a string, type
myString.toLowerCase();
java: To compare two numbers and return a boolean, type
1 > 2;
java: a class attribute is also called a
member variable
java: Member variable names are often prepended with
the letter “m” by convention
java: an alternative to console.printf(“string”); is
System.out.printf(“string”);
java: To create a public class with a public member variable, type
public class ClassName {
public String mMyString = "string";
}java: To make a classes member variable private, type
public class ClassName {
private String mMyString = "string";
}java: Making a member variable private
prevents access to it.
java: The only way to access or alter a private member variable is
to use a method that returns it
java: To create a method, type
public String getString() {
return mMyString;
}
java: methods that return a property of a class are often
prepended with “get”
java: methods that change a property of a class are often
prepended with “set”
java: To declare but not initialize a variable, type
public String myString;
java: To create a constructor method that takes a string argument upon instantiation, type
public ClassName(String myString) {
mMyString = myString;
}java: To instantiate a class, type
ClassName classNameInstance = new ClassName(param1);
java: Variables that do not change are called
constants
java: Constants are written by convention as
all caps separated by underscores.
java: the screen layouts are located in
main/res/layout
java: To create an integer variable that is a constant and cannot be changed, type
public final int MY_INT = 10;
java: A class level variable is
a member variable that can be accessed from the class without creating an instance
java: To create a class level variable, type
public static String myString = “string”;
java: To import a java file into the repl in order to access its classes, type
:load FileName.java
java: To access a class level variable, type
ClassName.mMemberVariable;
java: To access a class level method, type
ClassName.getMethod(param1);
java: To create a method that returns nothing, type
public void myMethod() {
}
java: final is usually
the last modifier before the Type
java: To create a class level method, type
public static String getString() {
return mMyString;
}
java: When you run a java file, it
searches the file for a static method named main and runs it.
java: To invert true, type
!true
java: post incrementing means
returning the value of the variable before incrementing it
java: pre incrementing means
returning the value of the variable after incrementing it
java: To post increment or decrement a variable, type
myInt++ or myInt–
java: To pre increment decrement a variable, type
++myInt or –myInt
java: To write a while loop, type
while (10 == 10) {
}
java: Multiple methods can
have the same name as long as their parameters are different
java: To raise an exception, type
throw new ExceptionName(“string”);
java: To create a try/catch block, type
try {
} catch(ExceptionName exVar) {
}
note: exVar is the variable that allows you to access attributes of the exception, like the message
java: In java, everything is
a class
java: To create a .java files main method, type
public class Filename {
public static void main (String[] args) {
...
}
}java: A char is
a data type that is one letter surrounded by single quotes
java: To return the index of a sub string, type
myString.indexOf(myChar);
java: if myString.indexOf(“string”); is not found
it returns -1
java: To concatenate a string and char, type
myString = myString + ‘a’;
or
myString += ‘a’;
java: To create an if and an else statement, type
if (10==10) {
} else {
}
java: You cannot pass myString.contains()
a char, because it is not converted
java: you can use myString.indexOf() on
a char, because it gets converted
java: To denote that a method is overriding a method inherited from a superclass, type
add the annotation @Override
