Get constructor by parameter type : Constructor « Reflection « Java Tutorial

1. Java Tutorial
2. Reflection
3. Constructor

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import static java.lang.System.out;

import java.lang.reflect.InvocationTargetException;

public class ConstructorTroubleAgain {
  public ConstructorTroubleAgain() {
  }

  public ConstructorTroubleAgain(Integer i) {
  }

  public ConstructorTroubleAgain(Object o) {
    out.format("Constructor passed Object%n");
  }

  public ConstructorTroubleAgain(String s) {
    out.format("Constructor passed String%n");
  }

  public static void main(String... args) {
    String argType = (args.length == 0 ? "" : args[0]);
    try {
      Class<?> c = Class.forName("ConstructorTroubleAgain");
      if ("".equals(argType)) {
        // IllegalArgumentException: wrong number of arguments
        Object o = c.getConstructor().newInstance("foo");
      } else if ("int".equals(argType)) {
        // NoSuchMethodException - looking for int, have Integer
        Object o = c.getConstructor(int.class);
      } else if ("Object".equals(argType)) {
        // newInstance() does not perform method resolution
        Object o = c.getConstructor(Object.class).newInstance("foo");
      } else {
        assert false;
      }

      // production code should handle these exceptions more gracefully
    } catch (ClassNotFoundException x) {
      x.printStackTrace();
    } catch (NoSuchMethodException x) {
      x.printStackTrace();
    } catch (InvocationTargetException x) {
      x.printStackTrace();
    } catch (InstantiationException x) {
      x.printStackTrace();
    } catch (IllegalAccessException x) {
      x.printStackTrace();
    }
  }
}