failingconstructor23.java

java编程思想第四版习题答案

// exceptions/FailingConstructor23.java
// TIJ4 Chapter Exceptions, Exercise 23, page 489
/* Add a class with a dispose() method to the previous exercise. Modify
* FailingConstructor so that the constructor creates one of these disposable
* objects, after which the constructor might through an exception, after which
* it creates a second disposable member object. Write code to properly guard
* against failure, and in main() verify that all possible failure situations
* are covered.
*/
// This solution satisfies the conditions called for in FailingConstructor23
// constructor, which catches its own exceptions.
import static org.greggordon.tools.Print.*;

class Disposable {
	private static int counter = 0;
	private int id = counter++;
	private boolean disposed;
	Disposable() {
		disposed = false;
	}
	void dispose() {
		disposed = true;
	}
	String checkStatus() {
		return (id + " " + (disposed ? "disposed" : "not disposed"));
	}
}

public class FailingConstructor23 {
	private Integer[] ia = new Integer[2];
	private static Disposable d0;
	private static Disposable d1;
	FailingConstructor23() throws Exception {
		try {
			d0 = new Disposable();
			try {
				ia[2] = 2; 	// causes exception thrown and
						// caught in middle try loop
				try {
					d1 = new Disposable();
				} catch(Exception e) {
					println("Caught e in inner try loop");
					e.printStackTrace(System.err);
					println("Failed to create d1");
				}
			} catch(Exception e) {
				println("Caught e in middle try loop");
				e.printStackTrace(System.err);
				println("Disposing d0");
				d0.dispose(); // d0 would have been created
				}
		} catch(Exception e) {
			println("Caught e in outer try loop");
			e.printStackTrace(System.err);
			println("Failed to create d0");
		}

	}
	public static void main(String[] args) {
		try {
			// the constructor catches its own exceptions:
			FailingConstructor23 fc = new FailingConstructor23();
		} catch(Exception e) {
			System.err.println("Caught Exception in main()");
			e.printStackTrace(System.err);
		}
	}
}