Java异常处理的探究

超、凢脫俗 2022-03-12 05:35 185阅读 0赞

//: exceptions/CleanupIdiom.java
    // Each disposable object must be followed by a try-finally
    
    class NeedsCleanup { // Construction can't fail
      private static long counter = 1;
      private final long id = counter++;
      public void dispose() {
        System.out.println("NeedsCleanup " + id + " disposed");
      }
    }
    
    class ConstructionException extends Exception {}
    
    class NeedsCleanup2 extends NeedsCleanup {
      // Construction can fail:
      public NeedsCleanup2() throws ConstructionException {}
    }
    
    public class CleanupIdiom {
      public static void main(String[] args) {
        // Section 1:
        NeedsCleanup nc1 = new NeedsCleanup();
        try {
          // ...
        } finally {
          nc1.dispose();
        }
    
        // Section 2:
        // If construction cannot fail you can group objects:
        NeedsCleanup nc2 = new NeedsCleanup();
        NeedsCleanup nc3 = new NeedsCleanup();
        try {
          // ...
        } finally {
          nc3.dispose(); // Reverse order of construction
          nc2.dispose();
        }
    
        // Section 3:
        // If construction can fail you must guard each one:
        try {
          NeedsCleanup2 nc4 = new NeedsCleanup2();
          try {
            NeedsCleanup2 nc5 = new NeedsCleanup2();
            try {
              // ...
            } finally {
              nc5.dispose();
            }
          } catch(ConstructionException e) { // nc5 constructor
            System.out.println(e);
          } finally {
            nc4.dispose();
          }
        } catch(ConstructionException e) { // nc4 constructor
          System.out.println(e);
        }
      }
    } /* Output:
    NeedsCleanup 1 disposed
    NeedsCleanup 3 disposed
    NeedsCleanup 2 disposed
    NeedsCleanup 5 disposed
    NeedsCleanup 4 disposed
    *///:~