design-pattern-java's Introduction

Design Pattern DEMO with Java

Behavioral

Chain Of Responsibility

Decouple sender and receiver from request
Runtime configuration
Hierarchical in nature
Be careful with long chain

Command

Encapsulate each request as an object
Decouple sender from processor
Few drawbacks
Often used for undo functionality

Interpreter 解譯器

Design

Context 待解譯的語句
AbstractExpression 所有規則都要實作的介面
Interpret(Context) with
- TerminalExpression 最小單位的規則
- NonterminalExpression 可以再展開的規則組合

Example in Java

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class InterpreterDemo {
    
    public static void main(String[] args) {
        String input = "Apple, orange, and lemons!";
        
        Pattern p = Pattern.compile("(orange|Orange|lemon|Lemon|apple|Apple|grape|Grape)");
        Matcher m = p.matcher(input);
        
        while (m.find()) {
            System.out.println("Found a " + m.group() + ".");
        }
    }
    
}

Iterator

Design

Interface based
Factory Method based
Independent, but fail fast
Enumerators are fail safe
Iterator, ConcreteIterator

Example in Java

import java.util.ArrayList;

public class IteratorDemo {
    public static void main(String[] args) {
        List<String> names = new ArrayList<>();

        names.add("Vincent");
        names.add("Ravi");
        names.add("Joan");

        Iterator<String> namesIterator = names.iterator();

        while(namesIterator.hasNext()) { 
            String name = namesIterator.next();
            System.out.println(name);
            namesIterator.remove();
        }
    }
}

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