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[add] add examples of type info
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‎java-base/src/main/java/com/brianway/learning/java/base/typeinfo/BoundedClassReferences.java

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package com.brianway.learning.java.base.typeinfo;
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public class BoundedClassReferences {
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public static void main(String[] args) {
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Class<? extends Number> bounded = int.class;
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bounded = double.class;
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bounded = Number.class;
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// Or anything else derived from Number.
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}
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} ///:~

‎java-base/src/main/java/com/brianway/learning/java/base/typeinfo/ClassCasts.java

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package com.brianway.learning.java.base.typeinfo;
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class Building {
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}
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class House extends Building {
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}
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public class ClassCasts {
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public static void main(String[] args) {
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Building b = new House();
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Class<House> houseType = House.class;
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House h = houseType.cast(b);
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h = (House) b; // ... or just do this.
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try {
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Class<House> hClass = House.class;
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//Produces exact type
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House house = hClass.newInstance();
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Class<? super House> up = hClass.getSuperclass();
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// won't compile:
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//Class<Building> up2 = hClass.getSuperclass();
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//Only produces Object
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Object obj = up.newInstance();
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System.out.println(house);
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System.out.println(obj);
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} catch (Exception e) {
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e.printStackTrace();
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}
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}
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} ///:~

‎java-base/src/main/java/com/brianway/learning/java/base/typeinfo/ClassInitialization.java

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package com.brianway.learning.java.base.typeinfo;
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import java.util.Random;
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/**
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* 1.仅使用.class语法来获得对类的引用不会引发初始化
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* 2."编译器常量",无需类初始化即可读取
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* 3.static final域不一定是编译器常量,static非final域一定不是
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*/
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public class ClassInitialization {
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public static Random rand = new Random(47);
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public static void main(String[] args) throws Exception {
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Class initable = Initable.class;
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System.out.println("After creating Initable ref");
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// Does not trigger initialization:
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System.out.println(Initable.staticFinal);
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// Does trigger initialization:
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System.out.println(Initable.staticFinal2);
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// Does trigger initialization:
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System.out.println(Initable2.staticNonFinal);
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Class initable3 = Class.forName("com.brianway.learning.java.base.typeinfo.Initable3");
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System.out.println("After creating Initable3 ref");
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System.out.println(Initable3.staticNonFinal);
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}
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}
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class Initable {
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static final int staticFinal = 47;
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static final int staticFinal2 =
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ClassInitialization.rand.nextInt(1000);
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static {
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System.out.println("Initializing Initable");
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}
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}
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class Initable2 {
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static int staticNonFinal = 147;
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static {
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System.out.println("Initializing Initable2");
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}
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}
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class Initable3 {
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static int staticNonFinal = 74;
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static {
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System.out.println("Initializing Initable3");
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}
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}
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/* Output:
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After creating Initable ref
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47
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Initializing Initable
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258
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Initializing Initable2
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147
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Initializing Initable3
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After creating Initable3 ref
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74
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*///:~

‎java-base/src/main/java/com/brianway/learning/java/base/typeinfo/FamilyVsExactType.java

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package com.brianway.learning.java.base.typeinfo;
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/**
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* The difference between instanceof and class.
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*/
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public class FamilyVsExactType {
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static void test(Object x) {
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System.out.println("Testing x of type " + x.getClass());
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System.out.println("x instanceof Base " + (x instanceof Base));
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System.out.println("x instanceof Derived " + (x instanceof Derived));
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System.out.println("Base.isInstance(x) " + Base.class.isInstance(x));
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System.out.println("Derived.isInstance(x) "
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+ Derived.class.isInstance(x));
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System.out.println("x.getClass() == Base.class "
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+ (x.getClass() == Base.class));
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System.out.println("x.getClass() == Derived.class "
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+ (x.getClass() == Derived.class));
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System.out.println("x.getClass().equals(Base.class)) "
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+ (x.getClass().equals(Base.class)));
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System.out.println("x.getClass().equals(Derived.class)) "
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+ (x.getClass().equals(Derived.class)));
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}
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public static void main(String[] args) {
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test(new Base());
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test(new Derived());
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}
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}
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class Base {
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}
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class Derived extends Base {
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}
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/* Output:
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Testing x of type class typeinfo.Base
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x instanceof Base true
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x instanceof Derived false
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Base.isInstance(x) true
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Derived.isInstance(x) false
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x.getClass() == Base.class true
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x.getClass() == Derived.class false
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x.getClass().equals(Base.class)) true
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x.getClass().equals(Derived.class)) false
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Testing x of type class typeinfo.Derived
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x instanceof Base true
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x instanceof Derived true
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Base.isInstance(x) true
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Derived.isInstance(x) true
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x.getClass() == Base.class false
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x.getClass() == Derived.class true
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x.getClass().equals(Base.class)) false
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x.getClass().equals(Derived.class)) true
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*///:~

‎java-base/src/main/java/com/brianway/learning/java/base/typeinfo/FilledList.java

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package com.brianway.learning.java.base.typeinfo;
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import java.util.ArrayList;
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import java.util.List;
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class CountedInteger {
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private static long counter;
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private final long id = counter++;
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public String toString() {
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return Long.toString(id);
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}
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}
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public class FilledList<T> {
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private Class<T> type;
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public FilledList(Class<T> type) {
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this.type = type;
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}
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public List<T> create(int nElements) {
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List<T> result = new ArrayList<T>();
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try {
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for (int i = 0; i < nElements; i++)
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result.add(type.newInstance());
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} catch (Exception e) {
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throw new RuntimeException(e);
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}
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return result;
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}
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public static void main(String[] args) {
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FilledList<CountedInteger> fl =
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new FilledList<CountedInteger>(CountedInteger.class);
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System.out.println(fl.create(15));
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}
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}
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/* Output:
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[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]
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*///:~

‎java-base/src/main/java/com/brianway/learning/java/base/typeinfo/GenericClassReferences.java

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package com.brianway.learning.java.base.typeinfo;
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public class GenericClassReferences {
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public static void main(String[] args) {
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Class<Integer> genericIntClass = int.class;
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genericIntClass = Integer.class; // Same thing
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Class intClass = int.class;
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intClass = double.class;
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// genericIntClass = double.class; // Illegal
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System.out.println(int.class == Integer.class);
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}
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} ///:~

‎java-base/src/main/java/com/brianway/learning/java/base/typeinfo/SimpleDynamicProxy.java

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package com.brianway.learning.java.base.typeinfo;//: typeinfo/SimpleDynamicProxy.java
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import java.lang.reflect.InvocationHandler;
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import java.lang.reflect.Method;
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import java.lang.reflect.Proxy;
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class DynamicProxyHandler implements InvocationHandler {
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private Object proxied;
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public DynamicProxyHandler(Object proxied) {
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this.proxied = proxied;
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}
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public Object
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invoke(Object proxy, Method method, Object[] args)
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throws Throwable {
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System.out.println("**** proxy: " + proxy.getClass().getSimpleName() +
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", method: " + method + ", args: " + args);
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if (args != null) {
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for (Object arg : args)
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System.out.println(" " + arg);
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}
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return method.invoke(proxied, args);
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}
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}
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class SimpleDynamicProxy {
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public static void consumer(Interface iface) {
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iface.doSomething();
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iface.somethingElse("bonobo");
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}
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public static void main(String[] args) {
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RealObject real = new RealObject();
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consumer(real);
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// Insert a proxy and call again:
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Interface proxy = (Interface) Proxy.newProxyInstance(
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Interface.class.getClassLoader(),
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new Class[] {Interface.class},
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new DynamicProxyHandler(real));
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consumer(proxy);
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}
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}
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/* Output: (95% match)
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doSomething
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somethingElse bonobo
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**** proxy: $Proxy0, method: public abstract void com.brianway.learning.java.base.typeinfo.Interface.doSomething(), args: null
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doSomething
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**** proxy: $Proxy0, method: public abstract void com.brianway.learning.java.base.typeinfo.Interface.somethingElse(java.lang.String), args: [Ljava.lang.Object;@d716361
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bonobo
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somethingElse bonobo
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*///:~

‎java-base/src/main/java/com/brianway/learning/java/base/typeinfo/SimpleProxyDemo.java

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package com.brianway.learning.java.base.typeinfo;
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interface Interface {
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void doSomething();
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void somethingElse(String arg);
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}
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class RealObject implements Interface {
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public void doSomething() {
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System.out.println("doSomething");
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}
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public void somethingElse(String arg) {
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System.out.println("somethingElse " + arg);
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}
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}
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class SimpleProxy implements Interface {
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private Interface proxied;
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public SimpleProxy(Interface proxied) {
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this.proxied = proxied;
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}
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public void doSomething() {
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System.out.println("SimpleProxy doSomething");
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proxied.doSomething();
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}
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public void somethingElse(String arg) {
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System.out.println("SimpleProxy somethingElse " + arg);
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proxied.somethingElse(arg);
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}
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}
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class SimpleProxyDemo {
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public static void consumer(Interface iface) {
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iface.doSomething();
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iface.somethingElse("bonobo");
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}
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public static void main(String[] args) {
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consumer(new RealObject());
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consumer(new SimpleProxy(new RealObject()));
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}
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}
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/* Output:
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doSomething
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somethingElse bonobo
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SimpleProxy doSomething
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doSomething
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SimpleProxy somethingElse bonobo
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somethingElse bonobo
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*///:~

‎java-base/src/main/java/com/brianway/learning/java/base/typeinfo/WildcardClassReferences.java

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package com.brianway.learning.java.base.typeinfo;
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public class WildcardClassReferences {
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public static void main(String[] args) {
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Class<?> intClass = int.class;
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intClass = double.class;
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}
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} ///:~

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