类型推断

提示

• Type Inference

无需指定类型参数名，编译器会自动推断类型的能力。

public class BoxDemo {

  public static <U> void addBox(U u,
      java.util.List<Box<U>> boxes) {
    Box<U> box = new Box<>();
    box.set(u);
    boxes.add(box);
  }

  public static <U> void outputBoxes(java.util.List<Box<U>> boxes) {
    int counter = 0;
    for (Box<U> box: boxes) {
      U boxContents = box.get();
      System.out.println("Box #" + counter + " contains [" +
             boxContents.toString() + "]");
      counter++;
    }
  }

  public static void main(String[] args) {
    java.util.ArrayList<Box<Integer>> listOfIntegerBoxes =
      new java.util.ArrayList<>();
    BoxDemo.<Integer>addBox(Integer.valueOf(10), listOfIntegerBoxes);
    BoxDemo.addBox(Integer.valueOf(20), listOfIntegerBoxes);
    BoxDemo.addBox(Integer.valueOf(30), listOfIntegerBoxes);
    BoxDemo.outputBoxes(listOfIntegerBoxes);
  }
}