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observer pattern
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‎RandomProblems/src/learnHeadFirstDesignPatterns/chapter_2_observer_pattern/CoreFamily.java

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package learnHeadFirstDesignPatterns.chapter_2_observer_pattern;
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public interface CoreFamily {
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public void registerRelative(Relative relative);
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public void removeRelative(Relative relative);
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public void notifyRelative();
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public void setCoreFamilyAttributes(String coreFamilyNames, int hikingTimes, int marriedMonths, String bibleReadingProgress);
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}

‎RandomProblems/src/learnHeadFirstDesignPatterns/chapter_2_observer_pattern/CoreFamilyImpl.java

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package learnHeadFirstDesignPatterns.chapter_2_observer_pattern;
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import java.util.ArrayList;
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import java.util.List;
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public class CoreFamilyImpl implements CoreFamily {
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private String coreFamilyName;
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private String bibleReadingProgress;
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private int monthsWeMarried;
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private int timesWeHiked;
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private List<Relative> relatives;
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public CoreFamilyImpl(String bibleReadingProgress, String coreFamilyName, int monthsWeMarried, int timesWeHiked) {
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this.relatives = new ArrayList<Relative>();
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this.bibleReadingProgress = bibleReadingProgress;
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this.coreFamilyName = coreFamilyName;
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this.monthsWeMarried = monthsWeMarried;
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this.timesWeHiked = timesWeHiked;
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}
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@Override
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public void registerRelative(Relative relative) {
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relatives.add(relative);
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}
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@Override
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public void removeRelative(Relative relative) {
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int i = relatives.indexOf(relative);
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if(i > 0){
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relatives.remove(i);
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}
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}
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@Override
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public void notifyRelative() {
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for(int i = 0; i < relatives.size(); i++){
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Relative relative = (Relative) relatives.get(i);
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relative.update(coreFamilyName, timesWeHiked, monthsWeMarried, bibleReadingProgress);
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}
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}
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public void hasUpdates(){
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notifyRelative();
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}
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@Override
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public void setCoreFamilyAttributes(String coreFamilyNames,
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int hikingTimes, int marriedMonths, String bibleReadingProgress) {
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this.coreFamilyName = coreFamilyNames;
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this.timesWeHiked = hikingTimes;
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this.monthsWeMarried = marriedMonths;
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this.bibleReadingProgress = bibleReadingProgress;
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hasUpdates();
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}
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}

‎RandomProblems/src/learnHeadFirstDesignPatterns/chapter_2_observer_pattern/ObserverPatternTestDrive.java

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package learnHeadFirstDesignPatterns.chapter_2_observer_pattern;
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/**NOTE: I didn't really implement the Observer pattern from Head First book here.
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* Just implemented the introduction part here. Could continue if interests arise in the future. - 10/04/2015*/
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/**
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* The Observer Pattern defines a one-to-many dependency between objects so that when one object changes state, all of its dependents are notified and updated automatically.
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*
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* Subjects + Observers = Observer Pattern */
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/**Design principle:
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* Strive for loosely coupled designs between objects that interact.*/
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public class ObserverPatternTestDrive {
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public static void main(String[] args) {
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CoreFamily coreFamily = new CoreFamilyImpl(" 1 Peter ", "Steve Sun & Sophie Yan", 1, 7);
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Relative eason = new RelativeImpl("Eason", coreFamily);
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coreFamily.registerRelative(eason);
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Relative motherInLaw = new RelativeImpl("Jinzhi Lin", coreFamily);
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coreFamily.registerRelative(motherInLaw);
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Relative fatherInLaw = new RelativeImpl("Jianlin Yan", coreFamily);
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coreFamily.registerRelative(fatherInLaw);
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coreFamily.setCoreFamilyAttributes("Sophie and Steve NEW NAME", 8, 2, "1 John");
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System.out.print("Program ended.");
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}
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}

‎RandomProblems/src/learnHeadFirstDesignPatterns/chapter_2_observer_pattern/Relative.java

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package learnHeadFirstDesignPatterns.chapter_2_observer_pattern;
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public interface Relative {
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public void update(String coreFamilyNames, int hikingTimes, int marriedMonths, String bibleReadingProgress);
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}

‎RandomProblems/src/learnHeadFirstDesignPatterns/chapter_2_observer_pattern/RelativeImpl.java

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package learnHeadFirstDesignPatterns.chapter_2_observer_pattern;
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public class RelativeImpl implements Relative {
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private String relativeName;
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private CoreFamily coreFamily;
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private String coreFamilyName;
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private String bibleReadingProgress;
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private int monthsWeMarried;
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private int timesWeHiked;
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public RelativeImpl(String relativeName, CoreFamily coreFamily) {
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this.relativeName = relativeName;
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this.coreFamily = coreFamily;
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}
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@Override
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public void update(String coreFamilyNames, int hikingTimes, int marriedMonths, String bibleReadingProgress) {
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System.out.print("Before updating:\n");
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display();
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this.bibleReadingProgress = bibleReadingProgress;
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this.coreFamilyName = coreFamilyNames;
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this.monthsWeMarried = marriedMonths;
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this.timesWeHiked = hikingTimes;
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System.out.print("After updating:\n");
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display();
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}
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private void display() {
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System.out.println("Current CoreFamilyAttributes are, coreFamilyName is: " + coreFamilyName + "\tbibleReadingProgress is: "
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+ bibleReadingProgress + "\tmonthsWeMarried is: " + monthsWeMarried + "\ttimesWeHiked is: " + timesWeHiked);
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}
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}

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