ex26(1).java

JAVA编程思想第四版英文原版习题答案. pdf原版的

// 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());	
	}	
}