arrayofgenerics10.java

Thinking In Java 第四版练习题答案

// arrays/ArrayOfGenerics10.java
// TIJ4 Chapter Arrays, Exercise 10, page 762
// Modify ArrayOfGeneric.java to use containers instead of arrays.
// Show that you can eliminate the compile-time warnings.
import java.util.*;

public class ArrayOfGenerics10 {
	@SuppressWarnings("unchecked")
	public static void main(String[] args) {
		List<List<String>> lls = new ArrayList<List<String>>();
		List<List> l = new ArrayList<List>();	
		// lls = (List<List<String>>)l; // error: inconvertible types
		lls.add(new ArrayList<String>());
		List<Object> lo = new ArrayList<Object>();
		// lo = lls; // error: incompatible types
		// Compile-time warning eliminated:
		List<List<BerylliumSphere>> llb = 
			new ArrayList<List<BerylliumSphere>>();
		for(int i = 0; i < 10; i++) {
			llb.add(new ArrayList<BerylliumSphere>());
				for(int j = 0; j < 2; j++)
					llb.get(i).add(new BerylliumSphere());
		}
		System.out.println(llb);	
	}
}