captureconversion.java

来自「Thinking in JAVA第四版源代码」· Java 代码 · 共 28 行

//: generics/CaptureConversion.java

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<Integer>(1);
    // f1(raw); // Produces warnings
    f2(raw); // No warnings
    Holder rawBasic = new Holder();
    rawBasic.set(new Object()); // Warning
    f2(rawBasic); // No warnings
    // Upcast to Holder<?>, still figures it out:
    Holder<?> wildcarded = new Holder<Double>(1.0);
    f2(wildcarded);
  }
} /* Output:
Integer
Object
Double
*///:~