48 lines
1.2 KiB
Java
48 lines
1.2 KiB
Java
// patterns/SingletonPattern.java
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// (c)2021 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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final class IntegerSingleton
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implements Resource<Integer> {
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private static IntegerSingleton value =
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new IntegerSingleton();
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private Integer i = Integer.valueOf(0);
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private IntegerSingleton() {
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System.out.println("IntegerSingleton()");
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}
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public static IntegerSingleton instance() {
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return value;
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}
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@Override public synchronized
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Integer get() { return i; }
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@Override public synchronized
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void set(Integer x) { i = x; }
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}
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public class SingletonPattern {
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public static <T> void show(Resource<T> r) {
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T val = r.get();
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System.out.println(val);
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}
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public static <T> void put(Resource<T> r, T val) {
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r.set(val);
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}
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public static void main(String[] args) {
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System.out.println("Inside main()");
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Resource<Integer> ir =
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IntegerSingleton.instance();
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Resource<Integer> ir2 =
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IntegerSingleton.instance();
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show(ir);
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put(ir2, Integer.valueOf(9));
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show(ir);
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}
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}
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/* Output:
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Inside main()
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IntegerSingleton()
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0
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9
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*/
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