OnJava8-Examples/generics/CaptureConversion.java at master · CSapprenticeWT/OnJava8-Examples · GitHub

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// generics/CaptureConversion.java

// We make no guarantees that this code is fit for any purpose.

// Visit http://OnJava8.com for more book information.

public class CaptureConversion {

static <T> void f1(Holder<T> holder) {

T t = holder.get();

System.out.println(t.getClass().getSimpleName());

}

static void f2(Holder<?> holder) {

f1(holder); // Call with captured type

}

@SuppressWarnings("unchecked")

public static void main(String[] args) {

Holder raw = new Holder<>(1);

f1(raw);

// warning: [unchecked] unchecked method invocation:

// method f1 in class CaptureConversion

// is applied to given types

// f1(raw);

// ^

// required: Holder<T>

// found: Holder

// where T is a type-variable:

// T extends Object declared in

// method <T>f1(Holder<T>)

// warning: [unchecked] unchecked conversion

// f1(raw);

// ^

// required: Holder<T>

// found: Holder

// where T is a type-variable:

// T extends Object declared in

// method <T>f1(Holder<T>)

// 2 warnings

f2(raw); // No warnings

Holder rawBasic = new Holder();

rawBasic.set(new Object());

// warning: [unchecked] unchecked call to set(T)

// as a member of the raw type Holder

// rawBasic.set(new Object());

// ^

// where T is a type-variable:

// T extends Object declared in class Holder

// 1 warning

f2(rawBasic); // No warnings

// Upcast to Holder<?>, still figures it out:

Holder<?> wildcarded = new Holder<>(1.0);

f2(wildcarded);

}

/* Output:

Integer

Object

Double

OnJava8-Examples/generics/CaptureConversion.java at master · CSapprenticeWT/OnJava8-Examples · GitHub

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