initial commit

StudyInterfaces/.classpath

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+<?xml version="1.0" encoding="UTF-8"?>
+<classpath>
+	<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-17">
+		<attributes>
+			<attribute name="module" value="true"/>
+		</attributes>
+	</classpathentry>
+	<classpathentry kind="src" path="src"/>
+	<classpathentry kind="output" path="bin"/>
+</classpath>

StudyInterfaces/.project

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+<?xml version="1.0" encoding="UTF-8"?>
+<projectDescription>
+	<name>StudyInterfaces</name>
+	<comment></comment>
+	<projects>
+	</projects>
+	<buildSpec>
+		<buildCommand>
+			<name>org.eclipse.jdt.core.javabuilder</name>
+			<arguments>
+			</arguments>
+		</buildCommand>
+	</buildSpec>
+	<natures>
+		<nature>org.eclipse.jdt.core.javanature</nature>
+	</natures>
+</projectDescription>

StudyInterfaces/.settings/org.eclipse.core.resources.prefs

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+eclipse.preferences.version=1
+encoding/<project>=UTF-8

StudyInterfaces/.settings/org.eclipse.jdt.core.prefs

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+eclipse.preferences.version=1
+org.eclipse.jdt.core.compiler.codegen.inlineJsrBytecode=enabled
+org.eclipse.jdt.core.compiler.codegen.targetPlatform=17
+org.eclipse.jdt.core.compiler.codegen.unusedLocal=preserve
+org.eclipse.jdt.core.compiler.compliance=17
+org.eclipse.jdt.core.compiler.debug.lineNumber=generate
+org.eclipse.jdt.core.compiler.debug.localVariable=generate
+org.eclipse.jdt.core.compiler.debug.sourceFile=generate
+org.eclipse.jdt.core.compiler.problem.assertIdentifier=error
+org.eclipse.jdt.core.compiler.problem.enablePreviewFeatures=disabled
+org.eclipse.jdt.core.compiler.problem.enumIdentifier=error
+org.eclipse.jdt.core.compiler.problem.reportPreviewFeatures=warning
+org.eclipse.jdt.core.compiler.release=enabled
+org.eclipse.jdt.core.compiler.source=17

StudyInterfaces/src/com/example/Exercise01.java

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+package com.example;
+
+public class Exercise01 {
+
+	public static void main(String[] args) {
+
+	}
+
+}
+
+interface A {
+}
+
+interface B {
+}
+
+interface C {
+}
+
+interface D extends A, B, C { // multiple inheritance
+}

StudyInterfaces/src/com/example/Exercise02.java

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+package com.example;
+
+public class Exercise02 {
+
+	public static void main(String[] args) {
+		DD o = new DD();
+		System.out.println(o instanceof DD);
+		System.out.println(o instanceof CC);
+		// Error : System.out.println(o instanceof AA);
+		System.out.println(o instanceof BB);
+	}
+
+}
+
+abstract class AA {}
+abstract class GG {}
+interface BB {}
+interface FF {}
+abstract class CC {}
+
+class DD extends CC implements BB, FF  {}

StudyInterfaces/src/com/example/Exercise03.java

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+package com.example;
+
+public class Exercise03 {
+	public static void main(String[] args) {
+
+	}
+}
+
+sealed interface Service permits ABC, XYZ {
+	int fun();
+}
+
+final class ABC implements Service {
+
+	@Override
+	public int fun() {
+		return 42;
+	}
+}
+
+final class XYZ implements Service {
+
+	@Override
+	public int fun() {
+		return 108;
+	}
+}

study-functional-programming/.classpath

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+<?xml version="1.0" encoding="UTF-8"?>
+<classpath>
+	<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-17">
+		<attributes>
+			<attribute name="module" value="true"/>
+		</attributes>
+	</classpathentry>
+	<classpathentry kind="src" path="src"/>
+	<classpathentry kind="output" path="bin"/>
+</classpath>

study-functional-programming/.project

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+<?xml version="1.0" encoding="UTF-8"?>
+<projectDescription>
+	<name>study-functional-programming</name>
+	<comment></comment>
+	<projects>
+	</projects>
+	<buildSpec>
+		<buildCommand>
+			<name>org.eclipse.jdt.core.javabuilder</name>
+			<arguments>
+			</arguments>
+		</buildCommand>
+	</buildSpec>
+	<natures>
+		<nature>org.eclipse.jdt.core.javanature</nature>
+	</natures>
+</projectDescription>

study-functional-programming/.settings/org.eclipse.core.resources.prefs

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+eclipse.preferences.version=1
+encoding/<project>=UTF-8

study-functional-programming/.settings/org.eclipse.jdt.core.prefs

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+eclipse.preferences.version=1
+org.eclipse.jdt.core.compiler.codegen.inlineJsrBytecode=enabled
+org.eclipse.jdt.core.compiler.codegen.targetPlatform=17
+org.eclipse.jdt.core.compiler.codegen.unusedLocal=preserve
+org.eclipse.jdt.core.compiler.compliance=17
+org.eclipse.jdt.core.compiler.debug.lineNumber=generate
+org.eclipse.jdt.core.compiler.debug.localVariable=generate
+org.eclipse.jdt.core.compiler.debug.sourceFile=generate
+org.eclipse.jdt.core.compiler.problem.assertIdentifier=error
+org.eclipse.jdt.core.compiler.problem.enablePreviewFeatures=disabled
+org.eclipse.jdt.core.compiler.problem.enumIdentifier=error
+org.eclipse.jdt.core.compiler.problem.reportPreviewFeatures=warning
+org.eclipse.jdt.core.compiler.release=enabled
+org.eclipse.jdt.core.compiler.source=17

study-functional-programming/src/com/example/DefineFunctionalProgramming.java

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+package com.example;
+
+import java.util.List;
+import java.util.function.Predicate;
+
+public class DefineFunctionalProgramming {
+
+	public static void main(String[] args) {
+		// fp's function: 1) higher-order function 
+		//                2) pure function -> immutable -> 
+		//                                   i. Lambda Expression
+		//                                  ii. Method Reference
+		var numbers = List.of(4, 8, 15, 16, 23, 42);
+		// even -> cube -> sum
+		// New Type: function -> functional interface -> Single Abstract Method
+		MyFun x = u -> 2 * u - 5 ; 
+
+		// Build-in Functional Interface: Predicate, Function, ...
+		Predicate<Integer> isEven = z -> z%2 == 0;
+		var result =
+		numbers.stream()
+		       //.filter(z -> z%2 ==0)  // 4  8    16   42
+		       .filter(MyFun::ciftMi)  // 4  8    16   42
+		       //.mapToInt(p -> p*p*p)        // 64 512  4096 74088
+		       .mapToInt(MyFun::kubu)        // 64 512  4096 74088
+		       // (0,64) -> 64 -> (64,512) -> 576 -> (576,4096) -> 4672 -> (4672,74088) -> 78760
+ 		       //.reduce(0, (s,r)->s+r); 
+		       //.reduce(0, Integer::sum);
+		       .sum();
+		System.out.println(result);
+	}
+
+}
+
+@FunctionalInterface
+interface MyFun {
+	int fun(int x);
+	static boolean ciftMi(int x) { return x%2 == 0;}
+	static int kubu(int x) {return x*x*x;}
+}