40 lines
947 B
Java
40 lines
947 B
Java
// generics/SelfBounding.java
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// (c)2017 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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class SelfBounded<T extends SelfBounded<T>> {
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T element;
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SelfBounded<T> set(T arg) {
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element = arg;
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return this;
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}
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T get() { return element; }
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}
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class A extends SelfBounded<A> {}
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class B extends SelfBounded<A> {} // Also OK
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class C extends SelfBounded<C> {
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C setAndGet(C arg) { set(arg); return get(); }
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}
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class D {}
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// Can't do this:
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// class E extends SelfBounded<D> {}
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// Compile error: Type parameter D is not within its bound
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// Alas, you can do this, so you cannot force the idiom:
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class F extends SelfBounded {}
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public class SelfBounding {
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public static void main(String[] args) {
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A a = new A();
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a.set(new A());
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a = a.set(new A()).get();
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a = a.get();
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C c = new C();
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c = c.setAndGet(new C());
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}
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}
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