?? ex26(1).java
字號:
// generics/Ex26.java
// TIJ4 Chapter Generics, Exercise 26, page 680
// Demonstrate array covariance using Numbers and Integers.
public class Ex26 {
public static void main(String[] args) {
Number[] numbers = new Integer[3];
numbers[0] = new Integer(0);
numbers[1] = new Integer(1);
numbers[2] = new Integer(2);
// Number abstract, cannot instantiate:
// numbers[0] = new Number();
try { // compile OK; runtime ArrayStoreException:
numbers[1] = new Double(3.4);
} catch(Exception e) {
System.out.println(e);
}
for(Number n : numbers)
System.out.println(n);
// compile errors: incompatible types:
// Integer[] ints = numbers;
// for(Integer n : numbers)
// System.out.println(n);
// even though runtime type is Integer:
for(Number n : numbers)
System.out.println(n.getClass().getSimpleName());
}
}
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