ex21(2).java

JAVA编程思想第四版英文原版习题答案. pdf原版的

// arrays/Ex21.java
// TIJ4 Chapter Arrays, Exercise 21, page 782
// Try to sort an array of the objects in Exercise 18. Implement 
// Comparable to fix the problem. Now create a Comparator to sort
// the objects into reverse order.
import java.util.*;
import net.mindview.util.*;
import static net.mindview.util.Print.*;

class CompBerylliumSphere 
	implements Comparable<CompBerylliumSphere> {
	private static long count;
	protected final long id = count++;
	public int compareTo(CompBerylliumSphere c2) {
		return (this.id < c2.id ? -1 : (this.id == c2.id ? 0 : 1));
	}
	
	public String toString() {
		return "BerylliumSphere " + id;
	}
}

class CompBerylliumSphereComparator 
	implements Comparator<CompBerylliumSphere> {
	public int compare(CompBerylliumSphere c1, CompBerylliumSphere c2) {
		return (c1.id > c2.id ? -1 : (c1.id == c2.id ? 0 : 1));
	}
}

public class Ex21 { 	
	public static void main(String[] args) {
		BerylliumSphere[] bsa = new BerylliumSphere[5];
		for(int i = 0; i < bsa.length; i++)
			bsa[i] = new BerylliumSphere();		
		// Arrays.sort(bsa); // runtime ClassCastException
		CompBerylliumSphere[] cbsa = new CompBerylliumSphere[5];
		for(int i = 0; i < cbsa.length; i++)
			cbsa[i] = new CompBerylliumSphere();
		print("unsorted:");
		print(Arrays.toString(cbsa));
		Arrays.sort(cbsa);
		print("sorted:");
		print(Arrays.toString(cbsa));
		Arrays.sort(cbsa, new CompBerylliumSphereComparator());
		print("reverse sorted:");
		print(Arrays.toString(cbsa));	
	}
}