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Polish Stage 7 Lesson 1
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‎「一入 Java 深似海 」/代码/segmentfault/deep-in-java/pom.xml

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<module>stage-3</module>
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<module>stage-4</module>
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<module>stage-5</module>
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<module>stage-7</module>
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</modules>
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<build>

‎「一入 Java 深似海 」/代码/segmentfault/deep-in-java/stage-7/pom.xml

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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<parent>
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<artifactId>deep-in-java</artifactId>
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<groupId>com.segmentfault</groupId>
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<version>1.0-SNAPSHOT</version>
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</parent>
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<modelVersion>4.0.0</modelVersion>
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<artifactId>stage-7</artifactId>
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<packaging>pom</packaging>
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<name>「一入 Java 深似海 」系列 :: 第七期</name>
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<modules>
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<module>stage-7-lesson-1</module>
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</modules>
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</project>

‎「一入 Java 深似海 」/代码/segmentfault/deep-in-java/stage-7/stage-7-lesson-1/pom.xml

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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<parent>
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<artifactId>stage-7</artifactId>
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<groupId>com.segmentfault</groupId>
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<version>1.0-SNAPSHOT</version>
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</parent>
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<modelVersion>4.0.0</modelVersion>
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<artifactId>stage-7-lesson-1</artifactId>
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<name>「一入 Java 深似海 」系列 :: 第七期 :: 第一节</name>
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</project>

‎「一入 Java 深似海 」/代码/segmentfault/deep-in-java/stage-7/stage-7-lesson-1/src/main/java/com/segmentfault/deep/in/java/reflection/AccessibleObjectDemo.java

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package com.segmentfault.deep.in.java.reflection;
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import java.lang.reflect.Method;
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import java.util.function.Consumer;
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import java.util.function.Supplier;
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public class AccessibleObjectDemo {
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public static void main(String[] args) throws Exception {
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// AccessibleObject 是 Field、Method 和 Constructor 父类
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// 访问性检查 isAccessible()
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// 修改访问性 setAccessible(boolean)
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String value = "Hello,World";
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execute(() -> value.toString());
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Method toStringMethod = String.class.getMethod("toString");
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// 预热
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execute(() -> {
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try {
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// 默认情况任何 AccessibleObject 对象都会做访问性检查
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toStringMethod.invoke(value);
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} catch (Exception e) {
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}
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});
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execute(() -> {
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try {
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// 默认情况任何 AccessibleObject 对象都会做访问性检查
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toStringMethod.setAccessible(true);
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toStringMethod.invoke(value);
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} catch (Exception e) {
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}
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});
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execute(() -> {
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try {
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// 默认情况任何 AccessibleObject 对象都会做访问性检查
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// 因此，关闭此检查，可以提升性能
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toStringMethod.setAccessible(false);
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toStringMethod.invoke(value);
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} catch (Exception e) {
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}
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});
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// 反射调用
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}
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private static void execute(Runnable runnable) {
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int times = 100000;
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long startTime = System.currentTimeMillis();
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for (int i = 0; i < times; i++) {
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runnable.run();
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}
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long costTime = System.currentTimeMillis() - startTime;
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System.out.printf("执行 %d 时间消耗：%d ms\n", times, costTime);
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}
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}

‎「一入 Java 深似海 」/代码/segmentfault/deep-in-java/stage-7/stage-7-lesson-1/src/main/java/com/segmentfault/deep/in/java/reflection/ClassMemberDemo.java

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package com.segmentfault.deep.in.java.reflection;
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public class ClassMemberDemo {
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class A {
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protected String value; // 一个类中可以定义唯一名称的字段
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}
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class B extends A {
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protected String value;
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}
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}

‎「一入 Java 深似海 」/代码/segmentfault/deep-in-java/stage-7/stage-7-lesson-1/src/main/java/com/segmentfault/deep/in/java/reflection/ClassObjectDemo.java

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package com.segmentfault.deep.in.java.reflection;
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import java.beans.ConstructorProperties;
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import java.io.Serializable;
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import java.lang.reflect.Modifier;
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import java.util.AbstractList;
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/**
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* Java 类对象
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*/
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public class ClassObjectDemo {
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public static void main(String[] args) {
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// Class 对象
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// 具体类对象
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// 没有这类方法 isConcrete 是否为具体类
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System.out.println(!Modifier.isAbstract(Object.class.getModifiers()));
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// 抽象类对象
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System.out.println(Modifier.isAbstract(AbstractList.class.getModifiers()));
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// 接口类对象
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System.out.println(Serializable.class.isInterface());
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// 枚举类对象
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System.out.println(Color.class.isEnum());
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// 注解类对象
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System.out.println(ConstructorProperties.class.isAnnotation());
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// 原生类对象
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System.out.println(int.class.isPrimitive());
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System.out.println(double.class.isPrimitive());
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// 数组类对象
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System.out.println(int[].class.isArray());
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System.out.println(Object[].class.isArray());
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// 特殊类型
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System.out.println(void.class);
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}
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}

‎「一入 Java 深似海 」/代码/segmentfault/deep-in-java/stage-7/stage-7-lesson-1/src/main/java/com/segmentfault/deep/in/java/reflection/Color.java

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package com.segmentfault.deep.in.java.reflection;
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public enum Color { // public enum Color = public final class Color extends java.lang.Enum
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RED, // RED = public static final Color = new Color("RED",1)
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YELLOW, // YELLOW = public static final Color = new Color("YELLOW",2)
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BLUE // BLUE = public static final Color = new Color("BLUE",3)
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}

‎「一入 Java 深似海 」/代码/segmentfault/deep-in-java/stage-7/stage-7-lesson-1/src/main/java/com/segmentfault/deep/in/java/reflection/JavaArrayDemo.java

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package com.segmentfault.deep.in.java.reflection;
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public class JavaArrayDemo {
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public static void main(String[] args) {
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int[] values = new int[0]; // 数组是 Java 对象
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// values.length; // length 字段也是虚拟机帮助提供
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// values 成员类型 = int.class
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}
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}

‎「一入 Java 深似海 」/代码/segmentfault/deep-in-java/stage-7/stage-7-lesson-1/src/main/java/com/segmentfault/deep/in/java/reflection/JavaClassMemberDemo.java

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package com.segmentfault.deep.in.java.reflection;
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import java.lang.reflect.Field;
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import java.util.Arrays;
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import java.util.Collections;
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import java.util.LinkedList;
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import java.util.List;
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import java.util.stream.Collectors;
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import java.util.stream.Stream;
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import static java.util.Arrays.asList;
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public class JavaClassMemberDemo {
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private int value;
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public static void main(String[] args) {
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// Java 类成员对象来自于 java.lang.Class
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// 成员访问性
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// 所有成员 getDeclaredXXX() ->
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// getDeclaredMethods()
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// getDeclaredFields()
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// getDeclaredConstructors
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// getDeclaredFields() - 所有声明的字段（仅限当前类） 与 getFields() - public 字段（仅限当前类）区别
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List<Field> allDeclaredFields = getAllDeclaredFields(ExtendedData.class);
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Field[] declaredFields = ExtendedData.class.getDeclaredFields();
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Field[] fields = ExtendedData.class.getFields();
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System.out.println("ExtendedData 类所有层次的声明字段 : " + allDeclaredFields.stream().map(Field::getName).collect(Collectors.joining(",")));
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System.out.println("ExtendedData 类所有的声明字段 : " + Stream.of(declaredFields).map(Field::getName).collect(Collectors.joining(",")));
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System.out.println("ExtendedData 类所有的 public 字段 : " + Stream.of(fields).map(Field::getName).collect(Collectors.joining(",")));
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}
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static List<Field> getAllDeclaredFields(Class<?> type) {
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if (Object.class.equals(type)) {
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return Collections.emptyList();
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}
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List<Field> allDeclaredFields = new LinkedList<>();
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Field[] declaredFields = type.getDeclaredFields();
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allDeclaredFields.addAll(asList(declaredFields));
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Class<?> superClass = type.getSuperclass();
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while (true) {
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if (superClass == null || Object.class.equals(superClass)) {
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break;
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}
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allDeclaredFields.addAll(getAllDeclaredFields(superClass));
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superClass = superClass.getSuperclass();
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}
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return allDeclaredFields;
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}
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public JavaClassMemberDemo() {
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}
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class Data {
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private int value;
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public int getValue() {
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return value;
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}
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protected void setValue(int value) {
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this.value = value;
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}
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}
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class ExtendedData extends Data {
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private String name;
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public void setName(String name) {
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this.name = name;
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}
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}
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}
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