GoF , . . .
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1) . . ;
2) . ;
3) . ;
4) .
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Creator GRASP.
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Abstract Factory ( ) (families of product objects);
Factory Method ( ) (subclass of object that is instantiated);
Builder () (how a composite object gets created);
Singleton () (the sole instance of a class);
Prototype () .
, , (class of object that is instantiated).
GoF , , .
:
Adapter () . (interface to an object);
Bridge () , (implementation of an object);
Composite () , (structure and composition of an object);
Decorator () . (responsibilities of an object without subclassing);
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Facade () (interface to a subsystem);
Flyweight () (storage costs of objects);
Proxy () (how an object is accessed... its location).
GoF .
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Chain of Responsibility ( ) - -, (object that can fulfill a request);
Command () , (when and how a request is fulfilled);
Iterator () , (how an aggregates elements are accessed, traversed);
Mediator () , , (how and which objects interact with each other);
Memento () (what private information is stored outside an object, and when);
Observer () (number of objects that depend on another object; how the dependent objects stay up to date);
State () (states of an object);
Strategy () (an algorithm);
Template Method ( ) , , (steps of an algorithm);
Visitor () , (operations that can be applied to object(s) without changing their class(es));
Interpreter () (grammar and interpretation of a language).
. Java Factory, Builder Chain of Responsibility.
Factory
, debug error . ILogger debug msg error msg, msg - , . , ILogger, ConsoleLoggerImpl FileLoggerImpl . Factory, getLogger FileLoggerImpl ConsoleLoggerImpl FileLogging = true ( false), logger.properties. true, getLogger FileLoggerImpl, ConsoleLoggerImpl. FactoryMethodPatternDemo Factory . . .
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ILogger.java
package by.bsac.patterns.factory;
public interface ILogger {
// Write out a debug message
public void debug(String msg);
// Write out an error message
public void error(String msg);
}
ConsoleLoggerImpl.java
package by.bsac.patterns.factory;
public class ConsoleLoggerImpl implements ILogger {
ConsoleLoggerImpl() {} // Not accessible from other packages!
public void debug(String msg) {
System.out.println("DEBUG: " + msg);
}
public void error(String msg) {
System.err.println("ERROR: " + msg);
}
}
FileLoggerImpl.java
package by.bsac.patterns.factory;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
public class FileLoggerImpl implements ILogger {
public void debug(String msg) {
try {
File file = new File("DebugLog.log");
// create file if doesn't exist
if (!file.exists()) {
file.createNewFile();
}
// true = append file
FileWriter fileWritter = new FileWriter(file.getName(), true);
BufferedWriter bufferWritter = new BufferedWriter(fileWritter);
bufferWritter.write("DEBUG:" + msg);
bufferWritter.close();
} catch (IOException e) {
e.printStackTrace();
}
}
public void error(String msg) {
try {
File file = new File("ErrorLog.log");
// create file if doesn't exist
if (!file.exists()) {
file.createNewFile();
}
// true = append file
FileWriter fileWritter = new FileWriter(file.getName(), true);
BufferedWriter bufferWritter = new BufferedWriter(fileWritter);
bufferWritter.write("ERROR:" + msg);
bufferWritter.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
Factory.java
package by.bsac.patterns.factory;
import java.io.IOException;
import java.util.Properties;
public class Factory {
public ILogger getLogger() {
if (isFileLoggingEnabled()) {
return new FileLoggerImpl();
} else {
return new ConsoleLoggerImpl();
}
}
// helper method, check if FileLogging is ON
// if so, log message to a file else print it to console.
private boolean isFileLoggingEnabled() {
Properties p = new Properties();
try {
p.load(getClass().getResourceAsStream("logger.properties"));
String fileLoggingValue = p.getProperty("FileLogging");
if ("true".equalsIgnoreCase(fileLoggingValue))
return true;
else
return false;
} catch (IOException e) {
return false;
}
}
}
