code manipulation : reflect(Class API)

code-manipulation/reflection-example/pom.xml

@@ -0,0 +1,30 @@
+<?xml version="1.0" encoding="UTF-8"?>
+
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <groupId>org.example</groupId>
+  <artifactId>reflection-example</artifactId>
+  <version>1.0-SNAPSHOT</version>
+
+  <name>reflection-example</name>
+  <!-- FIXME change it to the project's website -->
+  <url>http://www.example.com</url>
+
+  <properties>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    <maven.compiler.source>11</maven.compiler.source>
+    <maven.compiler.target>11</maven.compiler.target>
+  </properties>
+
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <version>4.11</version>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+
+</project>

code-manipulation/reflection-example/src/main/java/org/example/App.java

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+package org.example;
+
+import java.lang.reflect.Field;
+import java.lang.reflect.Modifier;
+import java.util.Arrays;
+
+public class App {
+    public static void main( String[] args ) throws ClassNotFoundException {
+
+
+        /**
+         * Class<T> 에 접근하여 정보 가져오기
+         */
+
+        // 메소드
+        Arrays.stream(Book.class.getDeclaredMethods()).forEach(m -> {
+            int modifiers = m.getModifiers();
+            System.out.println(m);
+            System.out.println(Modifier.isPrivate(modifiers));
+            System.out.println(m.getReturnType());
+        });
+
+
+
+//        // 접근지시자
+//        Arrays.stream(Book.class.getDeclaredFields()).forEach(f -> {
+//            int modifiers = f.getModifiers();
+//            System.out.println(f);
+//            System.out.println(Modifier.isPrivate(modifiers));
+//            System.out.println(Modifier.isStatic(modifiers));
+//        });
+
+
+//        // 메소드 가져오기
+//        Class<Book> bookClass = Book.class;
+//        System.out.println("getMethods() : Object 에서 상속받은 메소드도 가져온다.");
+//        Arrays.stream(bookClass.getMethods()).forEach(System.out::println);
+//
+//        System.out.println("===============================================");
+//
+//        System.out.println("getDeclaredMethods() : 인스턴스에 있는 메소드만 가져온다.");
+//        Arrays.stream(bookClass.getDeclaredMethods()).forEach(System.out::println);
+//
+//        System.out.println("===============================================");
+//
+//        System.out.println("getDeclaredConstructors() : 인스턴스에 있는 생성자를 가져온다.");
+//        Arrays.stream(bookClass.getDeclaredConstructors()).forEach(System.out::println);
+//
+//        System.out.println("===============================================");
+//
+//        System.out.println("getSuperclass() : 상속받은 부모클래스를 가져온다.");
+//        System.out.println(MyBook.class.getSuperclass());
+//
+//        System.out.println("===============================================");
+//
+//        System.out.println("getInterfaces() : 상속받은 인터페이스를 가져온다.");
+//        Arrays.stream(MyBook.class.getInterfaces()).forEach(System.out::println);
+
+
+//        // field 의 값을 가져오려면 생성한 인스턴스가 있어야 한다.
+//        Book book = new Book();
+//        Arrays.stream(book.getClass().getDeclaredFields())
+//                .forEach(f -> {
+//                    try {
+//                        f.setAccessible(true); // 모든 필드에 접근 가능
+//                        System.out.printf("%s, %s\n", f, f.get(book));
+//                    } catch (IllegalAccessException e) {
+//                        e.printStackTrace();
+//                    }
+//                });
+
+//        // 필드 가져오기
+//        Class<Book> bookClass = Book.class;
+//
+//        // getFields() -> public 만 접근
+//        Field[] fields = bookClass.getFields();
+//        Arrays.stream(fields).forEach(System.out::println);
+//
+//        System.out.println("===============================================");
+//
+//        // getDeclaredFields() -> 모든 필드 접근
+//        Field[] declaredFields = bookClass.getDeclaredFields();
+//        Arrays.stream(declaredFields).forEach(System.out::println);
+
+
+        /**
+         * Class<T> 에 접근하기
+         */
+
+
+//        // 클래시 로딩시 생성된 인스턴스로 접근
+//        Class<Book> bookClass = Book.class;
+//        System.out.println(bookClass.getName());
+//        System.out.println("============================");
+//
+//        // 생성한 인스턴스로 접근
+//        Book book = new Book();
+//        Class<? extends Book> bookClass1 = book.getClass();
+//        System.out.println(bookClass1.getName());
+//        System.out.println("============================");
+//
+//        // 문자열로 접근
+//        Class<?> bookClass2 = Class.forName("org.example.Book");
+//        System.out.println(bookClass2.getName());
+    }
+}

code-manipulation/reflection-example/src/main/java/org/example/Book.java

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+package org.example;
+
+public class Book {
+
+    private static String B = "BOOK";
+
+    private static final String C = "BOOK";
+
+    private String a = "a";
+
+    public String d = "d";
+
+    protected String e = "e";
+
+    public Book() {
+    }
+
+    public Book(String a, String d, String e) {
+        this.a = a;
+        this.d = d;
+        this.e = e;
+    }
+
+    private void f() {
+        System.out.println("f");
+    }
+
+    public void g() {
+        System.out.println("g");
+    }
+
+    public int h() {
+        return 100;
+    }
+}

code-manipulation/reflection-example/src/main/java/org/example/MyBook.java

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+package org.example;
+
+public class MyBook extends Book implements MyInterface{
+}

code-manipulation/reflection-example/src/main/java/org/example/MyInterface.java

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+package org.example;
+
+public interface MyInterface {
+}

code-manipulation/reflection-example/src/test/java/org/example/AppTest.java

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+package org.example;
+
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+/**
+ * Unit test for simple App.
+ */
+public class AppTest 
+{
+    /**
+     * Rigorous Test :-)
+     */
+    @Test
+    public void shouldAnswerWithTrue()
+    {
+        assertTrue( true );
+    }
+}