get Declared Method by name and parameter type : Method « Reflection « Java Tutorial

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import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class MethodTroubleReturns {
  private void drinkMe(int liters) {
    if (liters < 0)
      throw new IllegalArgumentException(
          "I can't drink a negative amount of liquid");
  }

  public static void main(String... args) {
    try {
      MethodTroubleReturns mtr = new MethodTroubleReturns();
      Class<?> c = mtr.getClass();
      Method m = c.getDeclaredMethod("drinkMe", int.class);
      m.invoke(mtr, -1);

      // production code should handle these exceptions more gracefully
    } catch (InvocationTargetException x) {
      Throwable cause = x.getCause();
      System.err.format("drinkMe() failed: %s%n", cause.getMessage());
    } catch (Exception x) {
      x.printStackTrace();
    }
  }
}