54 lines
1.4 KiB
Java
54 lines
1.4 KiB
Java
// containersindepth/CanonicalMapping.java
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// ©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://mindviewinc.com/Books/OnJava/ for more book information.
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// Demonstrates WeakHashMap.
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import java.util.*;
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class Element {
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private String ident;
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public Element(String id) { ident = id; }
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@Override
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public String toString() { return ident; }
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@Override
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public int hashCode() { return ident.hashCode(); }
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@Override
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public boolean equals(Object r) {
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return r instanceof Element &&
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ident.equals(((Element)r).ident);
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}
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@Override
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protected void finalize() {
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System.out.println("Finalizing " +
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getClass().getSimpleName() + " " + ident);
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}
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}
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class Key extends Element {
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public Key(String id) { super(id); }
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}
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class Value extends Element {
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public Value(String id) { super(id); }
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}
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public class CanonicalMapping {
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public static void main(String[] args) {
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int size = 1000;
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// Or, choose size via the command line:
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if(args.length > 0)
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size = new Integer(args[0]);
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Key[] keys = new Key[size];
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WeakHashMap<Key,Value> map = new WeakHashMap<>();
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for(int i = 0; i < size; i++) {
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Key k = new Key(Integer.toString(i));
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Value v = new Value(Integer.toString(i));
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if(i % 3 == 0)
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keys[i] = k; // Save as "real" references
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map.put(k, v);
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}
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System.gc();
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}
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}
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/* Output: (None) */
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