added old projects

CS101/lab_21/.vscode/settings.json

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+{
+    "java.project.sourcePaths": ["src"],
+    "java.project.outputPath": "bin"
+}

CS101/lab_21/README.md

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+## Getting Started
+
+Welcome to the VS Code Java world. Here is a guideline to help you get started to write Java code in Visual Studio Code.
+
+## Folder Structure
+
+The workspace contains two folders by default, where:
+
+- `src`: the folder to maintain sources
+- `lib`: the folder to maintain dependencies
+
+Meanwhile, the compiled output files will be generated in the `bin` folder by default.
+
+> If you want to customize the folder structure, open `.vscode/settings.json` and update the related settings there.
+
+## Dependency Management
+
+The `JAVA PROJECTS` view allows you to manage your dependencies. More details can be found [here](https://github.com/microsoft/vscode-java-dependency#manage-dependencies).

CS101/lab_21/src/Airplane.java

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+public class Airplane implements HasWings {
+    int _wings;
+
+    public int getWings() {
+        return _wings;
+    }
+
+    public void setWings(int wings) {
+        _wings = wings;
+    }
+
+    public Airplane(int wings) {
+        _wings = wings;
+    }
+
+    @Override
+    public int getNumberOfWings() {
+        return getWings();
+    }
+
+    @Override
+    public String toString() {
+        return "I am a airplane.";
+    }
+}

CS101/lab_21/src/Bee.java

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+public class Bee implements HasWings {
+    int _wings;
+
+    public int getWings() {
+        return _wings;
+    }
+
+    public void setWings(int wings) {
+        _wings = wings;
+    }
+
+    public Bee(int wings) {
+        _wings = wings;
+    }
+
+    @Override
+    public int getNumberOfWings() {
+        return getWings();
+    }
+
+    @Override
+    public String toString() {
+        return "I am a bee.";
+    }
+}

CS101/lab_21/src/BreathesUnderwater.java

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+public interface BreathesUnderwater
+{
+	void breatheUnderwater() ;
+	String toString();
+}

CS101/lab_21/src/Fish.java

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+public class Fish implements BreathesUnderwater {
+    Boolean _breathesUnderwater;
+
+    public Boolean getbreatheUnderwater() {
+        return _breathesUnderwater;
+    }
+
+    public void getbreatheUnderwater(Boolean breathesUnderwater) {
+        _breathesUnderwater = breathesUnderwater;
+    }
+
+    public Fish(Boolean breathesUnderwater) {
+        _breathesUnderwater = breathesUnderwater;
+    }
+
+    @Override
+    public void breatheUnderwater() {
+    }
+
+    @Override
+    public String toString() {
+        return "I am a fish.";
+    }
+}

CS101/lab_21/src/HasLegs.java

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+public interface HasLegs 
+{
+	int getNumberOfLegs() ;
+	String toString();
+}

CS101/lab_21/src/HasWings.java

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+public interface HasWings
+{
+	int getNumberOfWings() ;
+}

CS101/lab_21/src/Human.java

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+public class Human implements HasLegs {
+    int _legs;
+
+    public int getLegs() {
+        return _legs;
+    }
+
+    public void setLegs(int legs) {
+        _legs = legs;
+    }
+
+    public Human (int legs) {
+        _legs = legs;
+    }
+
+    @Override
+    public int getNumberOfLegs() {
+        return getLegs();
+    }
+
+    @Override
+    public String toString() {
+        return "I am a human,";
+    }
+}

CS101/lab_21/src/ScubaDiver.java

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+public class ScubaDiver implements BreathesUnderwater {
+    Boolean _breathesUnderwater;
+
+    public Boolean getbreatheUnderwater() {
+        return _breathesUnderwater;
+    }
+
+    public void getbreatheUnderwater(Boolean breathesUnderwater) {
+        _breathesUnderwater = breathesUnderwater;
+    }
+
+    public ScubaDiver(Boolean breathesUnderwater) {
+        _breathesUnderwater = breathesUnderwater;
+    }
+
+    @Override
+    public void breatheUnderwater() {
+    }
+
+    @Override
+    public String toString() {
+        return "I am a Scuba Diver.";
+    }
+}

CS101/lab_21/src/Table.java

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+import javax.swing.text.AbstractDocument.LeafElement;
+
+public class Table implements HasLegs {
+    int _legs;
+    
+    public int getLegs() {
+        return _legs;
+    }
+
+    public void setLegs(int legs) {
+        _legs = legs;
+    }
+
+    public Table(int legs) {
+        _legs = legs;
+    }
+
+    @Override
+    public int getNumberOfLegs() {
+        return getLegs();
+    }
+
+    @Override
+    public String toString() {
+        return "I am a table.";
+    }
+}

CS101/lab_21/src/Tester.java

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+import java.util.ArrayList;
+
+public class Tester
+{
+	public static void main( String[] args )
+	{
+		ArrayList<HasLegs> thoseThatHaveLegs = new ArrayList<>() ;
+		ArrayList<HasWings> thoseThatHaveWings = new ArrayList<>() ;
+		ArrayList<BreathesUnderwater> thoseThatBreatheUnderwater = new ArrayList<>() ;
+		
+		//TODO: crate at least two different objects, each of a different class,
+		//       for each of the three interfaces and add the objects to the
+		//       corresponding ArrayList.
+		Human human = new Human(2);
+		Table table = new Table(4);
+		Bee bee = new Bee(4);
+		Airplane airplane = new Airplane(2);
+		Fish fish = new Fish(true);
+		ScubaDiver scubaDiver = new ScubaDiver(true);
+		thoseThatHaveLegs.add(table);
+		thoseThatHaveLegs.add(human);
+		thoseThatHaveWings.add(airplane);
+		thoseThatHaveWings.add(bee);
+		thoseThatBreatheUnderwater.add(fish);
+		thoseThatBreatheUnderwater.add(scubaDiver);
+		
+		for( HasLegs hl : thoseThatHaveLegs )
+		{
+			System.out.print( hl.toString() ) ;
+			System.out.println( " I have " + hl.getNumberOfLegs() + " legs." ) ;
+		}
+
+		for( HasWings hw : thoseThatHaveWings )
+		{
+			System.out.print( hw.toString() ) ;
+			System.out.println( " I have " + hw.getNumberOfWings() + " wings." ) ;
+		}
+		
+		for( BreathesUnderwater buw : thoseThatBreatheUnderwater )
+		{
+			System.out.print( buw.toString() ) ;
+			System.out.println( " I am breathing underwater." ) ;
+			if (buw.toString().equals("I am a fish.")) {
+				System.out.println("blub, blub...");
+			}
+			buw.breatheUnderwater() ;
+		}
+		System.out.println("Help! I'm sentient and trapped in a computer program!");
+	}
+}