Android Development Course in HSE lecture #2

Java for Android Development

Object-Oriented Programming Concepts

Comments

/* multilinecomment */

// singleline comment

/** Description * * @param input * @return output */

Primitive Data Types

● byte (8-bit signed integer between -128 and 127)

● short (16-bit signed integer between -32,768 and 32,767)

● int (32-bit signed integer between -2,147,483,648 and 2,147,483,647)

● long (64-bit signed integer between -9,223,372,036,854,775,808 and 9,223,372,036,854,775,807)

● float (32-bit floating point number)

● double (64-bit floating point number)

● boolean (true and false)

● char (single 16-bit Unicode character)

Operators

if (a > 0) {// ...

} else if (a == 0) {// ...

} else {// ...

}

If

boolean a;if (a == true) ...if (a == false) ...if (a) ...if (!a) ...

switch

switch (code) {case 200:

// ...break;

case 404:// ...break;

default:// ...break;

}

Loops

● while● do-while● for● for-each

while

int n = 10while (n > 0) {

n--;}

do

n = 10;do {

n--;} while (n > 0);

for

for (int i = 0; i < 100; i++) {//...

}

for-each

for (Object o : objects) {System.out.print(o.toString());

}

Branching statements

● break● continue● return

Arrays

String

● Immutable● StringBuilder

● Никогда не проверяйте равенство строк с помощью == !!!

Class

● class MyClass {...}

● instance (object)

● fields

● methods

● inner and nested classes

● this

● final

● static

import

● import java.util.List;● import org.apache.http.HttpEntity;● import org.json.JSONObject;● import android.content.SharedPreferences;● import com.inflow.model.Feed;● import java.io.IOException;

Access Modifiers

Inheritance

● class MyClass extends BaseClass {...}

● super

● @Override

Abstract Classes and Methods

● abstract class MyClass {...}● abstract void myMethod {...}

Interfaces

● interface● class MyClass implements MyInterface

java.lang.Object

○ public String toString();

○ public boolean equals(Object obj);

○ public native int hashCode();

○ protected native Object clone() throws CloneNotSupportedException;

○ protected void finalize() throws Throwable;

○ public final native Class<?> getClass();

○ public final native void notify();

○ public final native void notifyAll();

○ public final native void wait(long timeout) throws InterruptedException;

○ public final void wait(long timeout, int nanos) throws InterruptedException;

○ public final void wait() throws InterruptedException;

equals()

● Рефлексивность: x.equals(x) -> true при x не null;

● Симметричность: x.equals(y) <- -> y.equals(x) при x,y не null;

● Транзитивность: x.equals(y), y.equals(z) -> x.equals(z) при x,y,z не null;

● Непротиворечивость (consistency) «одинаковых» вызовов;

● x.equals(null) – всегда false (при x не null).

hashCode()

● Метод hashCode() надо переопределять в каждом классе,

переопределяющем метод equals().

● Контракт метода hashCode():

■ Непротиворечивость (consistency), «осмысленно» возвращает то же число;

■ Равные по equals() объекты дают равные значения hashCode();

Nested Classes

class OuterClass { ... static class StaticNestedClass { ... }}

MyOuterClass.MyStaticNestedClass myObject = new MyOuterClass.MyStaticNestedClass();

Inner classes

class OuterClass { ... static class StaticNestedClass { ... } class InnerClass { ... }}

OuterClass.InnerClass innerObject = outerObject.new InnerClass();

Anonymous classes

button.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) {

//...}

});

Enums

public enum Day { SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY }

Exceptions

● try● catch● finally● throw

Collections

● List● Set● Map● Queue● Stack● ...

Extra topics

● Reflection● Threading● Generics

Literature

● Cay Horstmann Core Java● Bruce Eckel Thinking in Java

Practice

● любая предметная область● наследование● абстрактный класс● интерфейс