40 lines
1.4 KiB
Java
40 lines
1.4 KiB
Java
// understandingcollections/SpringDetector.java
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// (c)2016 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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// What will the weather be?
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import java.lang.reflect.*;
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import java.util.*;
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public class SpringDetector {
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// Uses a Groundhog or class derived from Groundhog:
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public static <T extends Groundhog>
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void detectSpring(Class<T> type) throws Exception {
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Constructor<T> ghog = type.getConstructor(int.class);
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Map<Groundhog,Prediction> map = new HashMap<>();
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for(int i = 0; i < 10; i++)
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map.put(ghog.newInstance(i), new Prediction());
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System.out.println("map = " + map);
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Groundhog gh = ghog.newInstance(3);
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System.out.println("Looking up prediction for " + gh);
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if(map.containsKey(gh))
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System.out.println(map.get(gh));
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else
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System.out.println("Key not found: " + gh);
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}
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public static void
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main(String[] args) throws Exception {
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detectSpring(Groundhog.class);
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}
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}
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/* Output:
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map = {Groundhog #2=Early Spring!, Groundhog #5=Early
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Spring!, Groundhog #6=Early Spring!, Groundhog #4=Early
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Spring!, Groundhog #9=Six more weeks of Winter!, Groundhog
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#8=Six more weeks of Winter!, Groundhog #0=Early Spring!,
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Groundhog #1=Early Spring!, Groundhog #3=Early Spring!,
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Groundhog #7=Six more weeks of Winter!}
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Looking up prediction for Groundhog #3
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Key not found: Groundhog #3
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*/
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