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Java_OOD Cheat Sheet Cheat Sheet (DRAFT) by

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Loops

for (int i: someArray) {}
while (somet­​hing) {}
do {somet­​hing} while (true)

Defining Variables

Defining new variable attributes
int x = 12;
int x; // will be defined as 0
Define by creating new instan​ces
String x = new String;

Condit­ionals

if statement
if (state­ment) {}
if-else statement
if (state­ment) {}
else{}

Switch Statement

switch (num) {
    case 1: doSomething ();
        break;
    default: doThis ();
        break;
}

Override

When you have inherit some of the class from
parents, but you want to do something different.
In override feature, all the subclass/class object
will use the newer method.
To make sure JDK knows what you are doing,
type @Override in front of the public name. If
the override is unsuccessful, JDK will returns
error.
Example of overriden helloWorld() method :

Class Student {
    public void helloWorld() {
        System.out.println("Hello");
    }
}

Class GradStudent extends Student

    @Override
    public void helloWorld() {
    System.out.println("Hello World");
    }
}

Rules of Overridden methods
1. Access modifier priority can only be
narrower or same as superclass
2. There is the same name method in
superclass / libraries
 

Prime Number Function

if (n < 2) { 
    return false; 
}
for (int i=2; i <= n/i; i++) {
    if (n%i == 0) { 
        return false;
    }
    return true;
}

Access Modifier

Attribute Modifier

ATTRIBUTE TYPE
ACCESS GRANTED
Private
Allows only in class where variables belong
Public
Allows any class to have this attribute
Protected
The methods or data members declared as protected are accessible within same package or sub classes in different package
Static
Attribute that depends on the class (not object)
Final
Defined once; does not allow any change­s/i­nhe­ritance

java.l­ang.String

Find the length -> int
 msg.length()
To lower/uppercase -> String
 msg.toLowerCase()
 msg.toUpperCase()
Replace a string -> String
 msg.replaceAll(String a, String b)
Split string between delimeter-> array
 msg.split(String delimeter)
Start/end with -> boolean
 msg.startsWith(String pre)
 msg.endsWith(String post)
String format -> String
 String.format(String format,
Object... args)
 

Interface

Interface is different from constr­​uctor. It consists of incomplete assign­​ments
Interface allows you to make sure that any inherited class will implement the methods
(It's like a contract to agree that this thing must be able to do this shit.) The method is then completed in the class that implements it.
Creating a new interf​ace

Constr­uctors

Constr­​uctors allow you to create an object
template. It consists of complete proced­​ures.
Create a blank constr­​uctor to allow its
extension classes to inherit this super
constr­​uctor.

<mo­dif­ier> Person () {}

Abstract

Abstract is a type of class but it can consist of
incomplete methods.

Create new abstract
<ac­ces­s_m­odi­fie­r> abstract class
HelloWorld () {}

Interface

Interface is different from constructor. It
consists of incomplete assignments
Interface allows you to make sure that any
inherited class can do the following methods.
The method is then completed in the class that implements it.

Creating a new interface

interface Bicycle {
    void speedUp (int increment);
}
----
    class funBike implements Bicycle {
         ...

        void speedUp (int increment)  {

            speed += increment;
       }
        ...
}

HashList

Methods
Descri­ption
void add (int index, Object element)
Add value to a list
Object remove(int index)
Remove item #index from list
Object get(int index)
Retreive item #index from list
void set(int index, Object element)
Set the data to correspond with #index