Read "Streaming Systems" 1&2, Streaming 101 Read "F1, a distributed SQL database that scales" Read "Zanzibar, Google’s Consistent, Global Authorization System" Read "Spanner, Google's Globally-Distributed Database" Read "Designing Data-intensive applications" 12, The Future of Data Systems IOS development with Swift Read "Designing Data-intensive applications" 10&11, Batch and Stream Processing Read "Designing Data-intensive applications" 9, Consistency and Consensus Read "Designing Data-intensive applications" 8, Distributed System Troubles Read "Designing Data-intensive applications" 7, Transactions Read "Designing Data-intensive applications" 6, Partitioning Read "Designing Data-intensive applications" 5, Replication Read "Designing Data-intensive applications" 3&4, Storage, Retrieval, Encoding Read "Designing Data-intensive applications" 1&2, Foundation of Data Systems Three cases of binary search TAMU Operating System 2 Memory Management TAMU Operating System 1 Introduction Overview in cloud computing 2 TAMU Operating System 7 Virtualization TAMU Operating System 6 File System TAMU Operating System 5 I/O and Disk Management TAMU Operating System 4 Synchronization TAMU Operating System 3 Concurrency and Threading TAMU Computer Networks 5 Data Link Layer TAMU Computer Networks 4 Network Layer TAMU Computer Networks 3 Transport Layer TAMU Computer Networks 2 Application Layer TAMU Computer Networks 1 Introduction Overview in distributed systems and cloud computing 1 A well-optimized Union-Find implementation, in Java A heap implementation supporting deletion TAMU Advanced Algorithms 3, Maximum Bandwidth Path (Dijkstra, MST, Linear) TAMU Advanced Algorithms 2, B+ tree and Segment Intersection TAMU Advanced Algorithms 1, BST, 2-3 Tree and Heap TAMU AI, Searching problems Factorization Machine and Field-aware Factorization Machine for CTR prediction TAMU Neural Network 10 Information-Theoretic Models TAMU Neural Network 9 Principal Component Analysis TAMU Neural Network 8 Neurodynamics TAMU Neural Network 7 Self-Organizing Maps TAMU Neural Network 6 Deep Learning Overview TAMU Neural Network 5 Radial-Basis Function Networks TAMU Neural Network 4 Multi-Layer Perceptrons TAMU Neural Network 3 Single-Layer Perceptrons Princeton Algorithms P1W6 Hash Tables & Symbol Table Applications Stanford ML 11 Application Example Photo OCR Stanford ML 10 Large Scale Machine Learning Stanford ML 9 Anomaly Detection and Recommender Systems Stanford ML 8 Clustering & Principal Component Analysis Princeton Algorithms P1W5 Balanced Search Trees TAMU Neural Network 2 Learning Processes TAMU Neural Network 1 Introduction Stanford ML 7 Support Vector Machine Stanford ML 6 Evaluate Algorithms Princeton Algorithms P1W4 Priority Queues and Symbol Tables Stanford ML 5 Neural Networks Learning Princeton Algorithms P1W3 Mergesort and Quicksort Stanford ML 4 Neural Networks Basics Princeton Algorithms P1W2 Stack and Queue, Basic Sorts Stanford ML 3 Classification Problems Stanford ML 2 Multivariate Regression and Normal Equation Princeton Algorithms P1W1 Union and Find Stanford ML 1 Introduction and Parameter Learning

Java Programming 2, Class

2017-05-19

Class, field and method

Constructor

  • Same name with class
  • No return value
    Person (String name, int age) {
        this.name = name;
        this.age = age;
    }

Access fields or methods

Person p = new Person();
System.out.println(p.name);
p.sayHello();

Overload

Several methods have the same name. They can be recognized while compiling.
Their signatures must be different:

  • Number of args
  • Type of args

this

Access fields and method in methods and constructor.

  • Can be used to distinguish fields and local variable this.name = name
  • Can be used to call another constructor this(0,""); inside a constructor
    • must be the first statement
void sayHello(){
    System.out.println("Hello! My name is " + name);
}
// is equivalent to
void sayHello(){
    System.out.println("Hello! My name is " + this.name);
}

Inheritance

  • Subclass
    • Can inherit and modify status and actions from superclass
    • Can add new status and actions
  • Superclass

Java support single inheritance. A class can only have one superclass.

Inheritance is achieved by extends. If no extends, this class is the subclass of java.lang.Object by default.

class Student extends Person {
    String school;
    int score;
    boolean isGood(){return score>80;}
}

Override

@Qverride
void sayHello(){
    System.out.println("Hello! I'm a Student. My name is " + name);
}

Overload

Overload will be a new added method.

Super

Can use super to access field and field of its superclass. (this can be used too)

  • To distinguish fields and methods with the same name between superclass and subclass
    • Even when the fields of superclass have been overridden. (super is required instead of this)
  • Can be used to utilize constructor of superclass
    • Constructor of superclass cannot be inherited.
    • In the constructor of subclass, can use super to call constructor of superclass
    • super() must be the first statement
void sayHello(){
    super.sayHello();
    System.out.println("I'm a Student.");
}
Student(String name, int age, String school){
    super(name, age);
    this.school = school;
}
  • An object of subclass can be an object of superclass
  • An object of superclass cannot be an object of subclass
  • If an arg is an object of superclass, then an object of subclass can be used here
  • Can use casting to convert reference of a superclass object to a reference of a subclass object
Person p = new Person();
Student s = new Student();
Person p2 = new Student();
Student s2 = (Student) p2;  // valid

Student s3 = (Student) p; // cannot be executed while compiling

Person [] manyp = new Person[ 100 ];
manyp[0] = new Person();
manyp[1] = new Student();   // valid

Packages

  • Namespace and path(folder)
  • Classes in the same package can access each other by default
  • Root path is determined by CLASSPATH

To avoid conflict of namespace and names.

package pkg1 [.pkg2];

import

Java compiler will import java.lang.* by default.

import pkg1 [.pkg2...].(classname |*);

import java.util.Date;
// so java.util.Date in program can be simplified as Date

// all classes on this level, not next level
import java.awt.*;
import java.awt.event.*;

Compile and run

javac -d destination_folder filename.java
javac -d . pk\*.java

// run class with main inside
java pk.Test

java -classpath classpath_name pk.Test

Modifiers

  • Access modifiers
    • public/private …
  • Other
    • abstract

Can be used on class and class members (fields and methods)

Modifiers Same Class Same package Subclass in different pkg non subclass in different pkg
private Yes      
default Yes Yes    
protected Yes Yes Yes  
public Yes Yes Yes Yes
  • public or default for class
  • setter and getter
    • private for fields
    • Use method setxxx and getxxx to set and get fields

Other

Other meaning for class? for member? for local var?
static static, not instance, class for inner class Yes  
final final, cannot be changed Yes Yes Yes
abstract abstract, cannot be instantiazed Yes Yes  

static:

  • The field for class, don’t belong to any instance
  • It’s saved in the memory area for class, instead of instance
  • Class variable can be accessed using class name or instance. Results are the same.
    • Person.totalNum or p.totalNum
  • Like in and out object of System class
  • Can be used as global variables
  • Cannot use this or super(because they are for an instance) in a static method
  • import static java.lang.System.*; So can use out.println();

final

  1. final class
    • This class cannot be inherited, no subclass
  2. final method
    • This method cannot be overriden by subclass
  3. final field and local variable
    • Their value cannot be changed (assign value once and only once)
    • static final will give a constant
      • Integer.MAX_VALUE, Math.PI
    • Assign value
      • No initial value given for static final, following will be assigned
        • num: 0
        • boolean: false
        • reference: null
      • If a final field (Not static), must be assigned value once and only once, cannot miss
        • Assign while defining
        • Assign in every constructor
      • final local var must be assigned value once and only once. The value may not be constant, but its value won’t change while it exists.

abstract

  1. abstract class
    • cannot be instantiated (new)
  2. abstract method
    • Abstract method defined a uniform interface for all subclass
    • Only need declaration, not realization, use semicolon ( ; ) not {}
    • abstract returnType abstractMethod( [paramlist] );
    • If a class has abstract method, it must be abstract class.
    • An abstract class is unnecessary to have abstract methods
    • Abstract method must be used(override) in subclass, otherwise the subclass will still be abstract
abstract class E{  
    public abstract void show();  
}  

class F extends E{  
    public void show(){  
        System.out.print("test all FFFF \n");  
    }  
}  

class G extends E{  
    public void show(){  
        System.out.print("test all GGGG \n");  
    }  
}  
public class main   
{  
    public static void main(String[] args)throws InterruptedException {  
        E p = new F();  
        p.show();  
        E q = new G();  
        q.show();  
    }  
}  

Interface

  • A kind of agreement
    • Declare: interface
      • All methods would be public abstract automatically
    • Use: implements
      • Multi inheritance
      • Unrelated with class inheritance
  • ‘Interface oriented programming’
  • Achieve the same action between several unrelated classes
  • Point out methods that several classes need to realize
  • Can understand the interface of an object, don’t need to know its class.
  • Reference type

Example

  • Interface: Flyable
  • Class: Bird(<-Animal), Plane(<-Vehicle), Superman(<-Animal)
  • Flyable f = new Bird();

  • Use public for methods while realization
  • Interface names should be end with ‘able or ‘ible’
  • Can have multi super interfaces

Declaration

[public] interface Collection [extends listOfSuperInterface] {
    void add (Object obj);
    void delete (Object obj);
    Object find (Object obj);
    int size ( );
}

Usage

class FIFOQueue implements collection{
    public void add(Object obj){
        ...
    }
    public void delete(Object obj){
        ...
    }
    public Object find(Object obj){
        ...
    }
    public int currentCount{
        ...
    }
}

reference

Collection c = new FIFOQueue();

c.add(obj);

constant

Declaration

type NAME = value;
  • The constant defined in a interface can be shared by the classes using this interface.
    • Same as #define in C and const in C++
    • the constant will be public, static, final

enum

Declaration

enum Light{ Red, Yellow, Green}

Usage

  • Light light = Light.Red;
  • switch( light ){case Red:... Break;}
  • The case should not be followed by Light.Red

Interface in Java8

The interface members can be

  • static method
    • non abstract
  • default method
    • provide a default version. Subclasses don’t need to write again in implements.

Syntax summary

class


[public] [abstact|final] class className[extends superclassName]
[implements InterfaceNameList]{
    //declare a class

    [public | protected | private] [static] [final] [transient] [volatile]type variableName;
    //declare variable, can be multiple

    [public | protected | private] [static] [final | abstract] [native] [synchronized]
    returnType methodName( [paramList] ) //declare method, can be multiple
    [throws exceptionList]{
        statements
    }
}

interface

[public] interface InterfaceName[extends superInterfaceList]{ //declaration of interface
    type constantName= Value; //constants
    returnType methodName( [paramList] ); //methods
}

Fixed declaration

// constructor
className([paramlist]){
    ...
}

// main()
public static void main( String args[]){
    ...
}

// finailize()
protected void finalize() throws throwable{
    ...
}

Source file

package packageName; //the package which the file belongs to,0 or 1

import packageName.[className|*]; //0 or more

public classDefinition//public class declaration, 0 or 1

interfaceDefinition and classDefinition//interface or class declaration, 0 or more
  • The name of source file must the the same as the public class name
  • At most 1 package statement or public class

Creative Commons License
Melon blog is created by melonskin. This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.
© 2016-2019. All rights reserved by melonskin. Powered by Jekyll.