92 lines
2.7 KiB
Java
92 lines
2.7 KiB
Java
// patterns/trash/Trash.java
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// (c)2020 MindView LLC: see Copyright.txt
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// We make no guarantees that this code is fit for any purpose.
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// Visit http://OnJava8.com for more book information.
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// Base class for Trash recycling examples
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package patterns.trash;
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import java.util.*;
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import java.lang.reflect.*;
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public abstract class Trash {
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private double weight;
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public Trash(double wt) { weight = wt; }
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public Trash() {}
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public abstract double value();
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public double weight() { return weight; }
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// Sums the value of Trash in a bin:
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static double val;
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public static <T extends Trash>
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void sumValue(List<? extends T> bin) {
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val = 0.0f;
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bin.forEach( t -> {
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val += t.weight() * t.value();
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System.out.println("weight of " +
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// RTTI gets type information
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// about the class:
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t.getClass().getName() +
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" = " + t.weight());
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});
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System.out.println("Total value = " + val);
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}
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@Override
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public String toString() {
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// Print correct subclass name:
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return getClass().getName() +
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" w:" + weight() + " v:" +
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String.format("%.2f", value());
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}
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// Remainder of class supports dynamic creation:
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public static class CannotCreateTrashException
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extends RuntimeException {
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public CannotCreateTrashException(Exception why) {
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super(why);
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}
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}
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public static class TrashClassNotFoundException
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extends RuntimeException {
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public TrashClassNotFoundException(Exception why) {
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super(why);
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}
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}
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public static class Info {
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public String id;
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public double data;
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public Info(String name, double data) {
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id = name;
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this.data = data;
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}
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}
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private static List<Class> trashTypes =
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new ArrayList<>();
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@SuppressWarnings("unchecked")
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public static <T extends Trash> T factory(Info info) {
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for(Class trashType : trashTypes) {
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// Determine the type and create one:
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if(trashType.getName().contains(info.id)) {
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try {
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// Get the dynamic constructor method
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// that takes a double argument:
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Constructor ctor =
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trashType.getConstructor(double.class);
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// Call the constructor to create a
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// new object:
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return (T)ctor.newInstance(info.data);
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} catch(Exception e) {
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throw new CannotCreateTrashException(e);
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}
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}
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}
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// The necessary Class was not in the list. Try to
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// load it, but it must be in your class path!
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try {
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System.out.println("Loading " + info.id);
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trashTypes.add(Class.forName(info.id));
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} catch(Exception e) {
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throw new TrashClassNotFoundException(e);
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}
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// Loaded successfully. Recursive call
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// should work this time:
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return factory(info);
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}
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}
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