fix rx java dep, add part4, progress

dev_projects/RxJava/RxJava/pom.xml

@@ -19,10 +19,23 @@
             rxjava
             https://mvnrepository.com/artifact/io.reactivex/rxjava
         -->
+<!--        <dependency>-->
+<!--            <groupId>io.reactivex</groupId>-->
+<!--            <artifactId>rxjava</artifactId>-->
+<!--            <version>1.3.8</version>-->
+<!--        </dependency>-->
+
+        <!-- https://mvnrepository.com/artifact/com.netflix.rxjava/rxjava-core -->
+        <dependency>
+            <groupId>com.netflix.rxjava</groupId>
+            <artifactId>rxjava-core</artifactId>
+            <version>0.20.7</version>
+        </dependency>
+
         <dependency>
-            <groupId>io.reactivex</groupId>
+            <groupId>io.reactivex.rxjava3</groupId>
             <artifactId>rxjava</artifactId>
-            <version>1.3.8</version>
+            <version>3.1.6</version>
         </dependency>
 
     </dependencies>

dev_projects/RxJava/RxJava/src/main/java/com/yen/courseV1/part3.java

@@ -6,9 +6,9 @@
 import java.util.Scanner;
 import java.util.concurrent.TimeUnit;
 import javax.swing.*;
-import rx.Completable;
+
+import io.reactivex.rxjava3.core.Completable;
 import rx.Observable;
-import rx.functions.Action0;
 
 public class part3 {
   public static void main(String[] args) {
@@ -36,6 +36,7 @@ public static void main(String[] args) {
           System.out.println("5 sec passed " + item);
         });
 
+    // TODO : FIX BELOW
     //Action action2 = () -> System.out.println("hello world!!");
     Action action =
         new AbstractAction() {
@@ -45,7 +46,7 @@ public void actionPerformed(ActionEvent e) {
           }
         };
 
-    Completable completable = Completable.fromAction((Action0) action);
+    Completable completable = Completable.fromAction((io.reactivex.rxjava3.functions.Action) action);
 
     completable.subscribe(() -> {
         System.out.println("---> Action ends");

dev_projects/RxJava/RxJava/src/main/java/com/yen/courseV1/part4.java

@@ -0,0 +1,104 @@
+package com.yen.courseV1;
+
+// https://youtu.be/EIwAerzQDvA?si=NQNL6Lgl9tc9qsU8
+
+import io.reactivex.rxjava3.annotations.NonNull;
+import io.reactivex.rxjava3.core.Maybe;
+import io.reactivex.rxjava3.core.MaybeObserver;
+import io.reactivex.rxjava3.core.Single;
+import io.reactivex.rxjava3.core.SingleObserver;
+import io.reactivex.rxjava3.disposables.Disposable;
+
+
+public class part4 {
+  public static void main(String[] args) {
+
+      /** Example 1 : Single
+       *
+       *  Single : ONLY emit once and ONLY one item, other situation treated as error
+       */
+      //  Single<String>, NOTE how this different from regular Obervable
+      Single<String> single = createSingle();
+      single.subscribe(new SingleObserver<String>(){
+          @Override
+          public void onSubscribe(@NonNull Disposable d) {
+
+          }
+
+          @Override
+          public void onSuccess(@NonNull String s) {
+              System.out.println("(onSuccess) s = " + s);
+          }
+
+          @Override
+          public void onError(@NonNull Throwable e) {
+              System.out.println("(onError) = " + e.getMessage());
+          }
+      });
+
+      /** Example 2 : Maybe
+       *
+       *  Maybe : emit one or no item
+       */
+
+      // Maybe
+      Maybe<String> maybe = createMaybe();
+
+      maybe.subscribe(new MaybeObserver<String>() {
+          @Override
+          public void onSubscribe(@NonNull Disposable d) {
+
+          }
+
+          @Override
+          public void onSuccess(@NonNull String s) {
+              System.out.println("(onSuccess) s = " + s);
+          }
+
+          @Override
+          public void onError(@NonNull Throwable e) {
+              System.out.println("(onError) = " + e.getMessage());
+          }
+
+          @Override
+          public void onComplete() {
+              System.out.println("completed! no new content");
+          }
+      });
+
+  }
+
+    public static Single<String> createSingle(){
+        return Single.create(emitter -> {
+            String user = fetchUser();
+            if (user != null){
+                emitter.onSuccess(user);
+            }else{
+                emitter.onError(new Exception("user not found"));
+            }
+        });
+    }
+
+    public static String fetchUser(){
+      //return "May";
+      return null;
+    }
+
+    public static Maybe createMaybe(){
+      return Maybe.create(emitter -> {
+          String newContent = readFile();
+          if (newContent != null){
+              emitter.onSuccess(newContent);
+          }else{
+              emitter.onComplete();
+          }
+      });
+    }
+
+    public static String readFile(){
+      //return "content of some file";
+      return null;
+    }
+
+}
+

dev_projects/RxJava/progress.txt

@@ -3,4 +3,6 @@
 ## 20240719
 - https://youtu.be/7mbjhNCWqvs?si=GtCY3Wk5AFTdjYgS
 - https://youtu.be/ApUUN55V2RE?si=zOpzZ14He9IzmqGZ
-- https://youtu.be/ApUUN55V2RE?si=ZpZ6K7coesyXk3nO
+- https://youtu.be/ApUUN55V2RE?si=ZpZ6K7coesyXk3nO
+- https://youtu.be/EIwAerzQDvA?si=RufdyI47fIpTJ0JU
+- https://youtu.be/EIwAerzQDvA?si=YyLHTw7Wut_qw8QZ