63 lines
1.7 KiB
Java
63 lines
1.7 KiB
Java
// generics/CaptureConversion.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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public class CaptureConversion {
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static <T> void f1(Holder<T> holder) {
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T t = holder.get();
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System.out.println(t.getClass().getSimpleName());
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}
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static void f2(Holder<?> holder) {
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f1(holder); // Call with captured type
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}
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@SuppressWarnings("unchecked")
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public static void main(String[] args) {
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Holder raw = new Holder<>(1);
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f1(raw);
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// warning: [unchecked] unchecked method invocation:
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// method f1 in class CaptureConversion
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// is applied to given types
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// f1(raw);
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// ^
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// required: Holder<T>
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// found: Holder
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// where T is a type-variable:
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// T extends Object declared in
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// method <T>f1(Holder<T>)
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// warning: [unchecked] unchecked conversion
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// f1(raw);
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// ^
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// required: Holder<T>
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// found: Holder
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// where T is a type-variable:
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// T extends Object declared in
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// method <T>f1(Holder<T>)
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// 2 warnings
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f2(raw); // No warnings
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Holder rawBasic = new Holder();
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rawBasic.set(new Object());
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// warning: [unchecked] unchecked call to set(T)
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// as a member of the raw type Holder
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// rawBasic.set(new Object());
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// ^
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// where T is a type-variable:
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// T extends Object declared in class Holder
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// 1 warning
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f2(rawBasic); // No warnings
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// Upcast to Holder<?>, still figures it out:
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Holder<?> wildcarded = new Holder<>(1.0);
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f2(wildcarded);
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}
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}
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/* Output:
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Integer
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Integer
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Object
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Double
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*/
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