Review notes

Characteristics of Java

Simple, object oriented,robust, secure, architecture neutral and portable, high proformance,interpreted dynamic, distributed.
write once, run everywhere

how java works

To compile, use javac XXX.java.
To run, use java XXX .
Not every program has a main method.
You compile the program into bytecode.
The bytecode is interpreted by Java virtual machine.

Comments

There are 3 differenet kind of comments.

// : single line
/* ....... */ : multiple lines.
/** ...... */ : multiple lines, can be used to generate documementation.
You should know the difference between them and how to use them.

main

public static void main(String[] args)
It is the entry point of an application.
Not every class has this method. If you has this method in the class, you can run the program by java ClassName .
You can overload the main method. But it is not the entry point of the application.
This method is a class method, with argument of type String[]. The return tpye is void. It is no different from other methods.
Since args is a String array. You can use
- args.length to access the length of args.
- You can use args[0], args[1]... to access the elements in the array
- If you try to access a non-existent args[i] (i.e. i >= args.length ) an error will occur during runtime.

In more detail :

you run java ClassName string0 string1 ..
String[] args = {string0, string1 , ... } is created
args pass to main(String[] args) and the method body is executed
if no argument is given, args is a null .
arguments are seperated by space
if you want to have an arguemnt with space in between use quotation. e.g. java ClassName "Charles Li".

System.out.println(String s)

Use System.out.println(string) to print out a string and then go to next line.
Use System.out.print(String) to print out a string without going to a new line at the end.
System.out.println(....) can print out int, float,... as well.

class

Objects has states(members) and behavior(methods)
Everything in java is a class.
The filename must be the classname.java

Identifies

Identifies are used to name class, methods, variables.
Not all characters can form an indentify. In below are the basic rules

An identify is a squence of letters , digits, dollar sign $, underscore _.
It cannot begin with a digit.
It cannot be any reserved keywords like , public, class, void ....
Actually it can be in other language (other than English) if you use unicode.
They are case senstive . i.e. myName is different from MyName.

Primitive type

Primitive types are byte, short, int, long, float, double, char, boolean.
You don't have to memorize the size of the primitive. But you should know that they are platform independent. And long is more precise than int, double is more precise than float etc etc.
You can define more than more than one variable of the same primitive on the same line, eg.
```
 int a, b, c
```

int

If you don't initiate the value for an integer, it is 0
You dont't need to understand the octal number and hexadecimal number. They won't appear in the midterm

float and double

Different ways to declare double are

 double a = 3.14, b = 3, c = 2.713e10, d = 34.665e5d;

Ways to declare float are very similar to double. You have to add f at the end of the number.
```
float a = 3.14f, b= 34.665e5f;
```
If you don't initate the values, they are 0.
float a = 3.14 causes an compiling error because 3.14 is a double by defalt

long

The way to declare it is long x = 58819394L; .
more precious then int

char

char represents a character.
example char a = 'a';

boolean

example
```
boolean a = true;
boolean b = false;
```

Arithemetic

You should know how to do arithemetic on primitive type.
The arithmetic operators are very similar to C++.
When the operands are of 2 different types, the more precious type will be returned.
example : when a integer add to a float, the result is a float.

Flow control

Refer to my notes on flow control for more detail
you should know how to use if, else, while, do-while, for, switch .
You should skip the parts on break and continue

Array

To declare an array use ClassName[] arrayName
To allocate an array with given size, use arrayName = new ClassName[size].
You should initiate the elements of the array, otherwise they all are null.

A quick way to initalize array is :
Example

 
int[] array1 = {1,2,3,4,5};
String[] array2 = {"this", "is" , "review" , "notes"}

use array.length to get the size of the array.
Try to understand arrays of array from my handout

String

initiate String by String s = "Hi";
You can add 2 strings together by +
You should not memorize all the methods in the String class. But you should understand the methods. Documentation will be provided if I ask questions on this class.

class and inheritance

You have to know all the material in my handout. This includes

how to use constructor.
how to use new.
how to use private, protected and public and their meaning.
understand the difference between static variables and non-static variables.
how to use this and super.
understand overriding and overloading
understand 3 ways to use final.
understand subclass and superclass and how to extends classes.
understand how Java pass information in a method. Java pass the arguments by value.

Swing

Layout

3 layouts. BorderLayout, GridLayout, FlowLayout
You should know the effect of different layout
You should know how to add, insert and remove components.

BorderLayout

You should remember all the constructor.

Use BorderLayout.NORTH, BorderLayout.SOUTH,... to specific the direction.

use add(component) or

 add(component,
BorderLayout.CENTER)

to add to the center.

use add(component, BorderLayout.NORTH) etc to add to the north

use remove(int) to remove

JFrame

The default layout is BorderLayout.
we don't add components directly to JFrame. insteand we use getContentPane().add(...) to add components. or getContentPane().setLayout(..) to set layout.
you should know how to use setSize, pack, setVisible, setLocation, setBackground and all other methods I mentioned in the handout.

JPanel

You should remember all the constructors.
Unlike JFrame, we can add components to it directly.
You should remember all the methods given in my handout.

JButton, JLabel

You should know how to create an ImageIcon and set the image icon.
remember all the constructors and methods given in my handout.

JFrame

Useful methods

`JFrame(), JFrame(String title)`	two useful constructors.
`getContentPane()`	you `getLayout` and `add, remove` through the `contentPane`.
`setVisible(boolean)`	set the frame visible
`setSize(int width,int height)`	set the dimension of the frame
`pack()`	use the most "prefect" size for the frame.
`setLocation(int x, int y)`	Set the location of the upper left corner at (x,y). The upper left corner of you screen is (0,0)

Attention:

setLayout , add and remove has to be used through getContentPane().
If you add/remove/setLayout without getContentPane(), it will be a compiling error.
the default layout for JFrame is BorderLayout

JPanel

`JPanel(),JPanel(LayoutManager)`	constructors
`void add(Component),void add(Component, int), void remove(int)`	add, remove components
`void setLayout(LayoutManager),LayoutManager getLayout()`	the meaning is obvious

Attention

Unlike JFrame, the class use add, remove, setLayout directly.
The default layout is FlowLayout
You can use it as intermediate container to hold other componenets (refer to my notes.
or you can extends it to create some complicated components.

Layout

Set the layout of JFrame throught getContentPane().setLayout(....)
set the layout of JPanel by setLayout().

BorderLayout

constructors
BorderLayout(), BorderLayout(int hgap,vgap). The gap is 0 if you don't specify them
add, remove

add(Component comp, int direction), remove(int direction): direction can be BorderLayout.NORTH,....

add(Component comp): add the CENTER

Attention
You should know how the output look like if you just add components to north, center, east? what is the output if you just add to north, south and center? Try different combinations.

FlowLayout

Refer to my handout for 3 constructors.
The default alignment for FlowLayout is CENTER
And the default gap is 5.
you should know the meaning of index in add(comp,index), remove(index)

GridLayout

Refer to my handout for 2 constructors.
you should know the meaning of index in add(comp,index), remove(index)
You should know what happen when we set row = 0 or col = 0.

Pass by reference