methods

问题 I have just started programming some things with Greenfoot, learning java along the way. I have become familiar on how to call certain methods between classes, and also differences between static and non-static. I'm makeing a game where you play the crab and move around to collect worms. There is a lobster that randomly roams around and if comes in contact with the crab, the crab dissapears. Every time you eat a worm, the score goes up by 10. It contains 5 classes named Crab, Lobster, Worm,

问题 I am trying to use a variable from a method I created in another class in the main section. For example: public class test { public static int n; public void getLower(){ int p = 12; } public static void main(String[] args) { test example = new test(); example.getLower(); System.out.println(p); } } However, I get the error message 'p cannot be resolved to a variable'. Is what I'm trying to do possible? Thanks in advance! 回答1: p is a local variable within the getLower method. You're not

问题 I am running Rails 3.1.1 and getting this error when running this command. Obviously new to Rails, any help appreciated: rake aborted! undefined method `prerequisites' for nil:NilClass /Users/220040168/.rvm/gems/ruby-1.9.2-p290@rails3tutorial/gems/rspec-rails-2.6.0/lib/rspec/rails/tasks/rspec.rake:3:in `<top (required)>' /Users/220040168/.rvm/gems/ruby-1.9.2-p290@rails3tutorial/gems/rspec-rails-2.6.0/lib/rspec-rails.rb:10:in `load' /Users/220040168/.rvm/gems/ruby-1.9.2-p290@rails3tutorial

问题 I have some void methods which are static. Is it better to pass variables by reference or by value, because I'm passing large amount of text into these variables : public static void renderText(ref StringBuilder build) { //Do your job. } So could someone explain me, what happens when I send a reference of StringBuilder , does it only access this StringBuilder ? (It does not copy it right!). And just in case I'm not changing the value or any other property of input arguments into methods. So,

问题 I have some void methods which are static. Is it better to pass variables by reference or by value, because I'm passing large amount of text into these variables : public static void renderText(ref StringBuilder build) { //Do your job. } So could someone explain me, what happens when I send a reference of StringBuilder , does it only access this StringBuilder ? (It does not copy it right!). And just in case I'm not changing the value or any other property of input arguments into methods. So,

问题 I'm supposed to make a code in Java out of the following class diagram. In the description of my assignment the following is stated; "One thing is completely missing from the class diagram, methods for updating the attributes. This is because the client of the system has decided that it is not allowed to update them. However, we know that this requirement will change, at least for age. The task therefore also includes designing and implementing a method for updating the age. When you do so,

问题 I'm trying to call the java code from S. This method call: cls = (* env) -> FindClass (env, "org / libsdl / app / SDLActivity"); mid = (* env) -> GetStaticMethodID (env, cls, "play", "([Ljava / lang / String;) V"); (* env) -> CallVoidMethod (env, cls, mid); java method: public static void play () { track.write (bytes, 0, bytes.length); } Cause this error: 03-25 18:17:32.313: WARN / dalvikvm (655): JNI WARNING: JNI method called with exception raised 03-25 18:17:32.313: WARN / dalvikvm (655):

问题 I want to do something like class A { def f1: Unit = ... def f2: Unit = ... } def foo(f: => Unit) { (new A).f // ??? } where f is supposed to be a member function of class A. I believe the standard solution is def foo(f: A => Unit) { f(new A) } and use it in this way foo(_.f1) foo(_.f2) But now I can pass in an arbitrary function that has this signature, which may be not desired. Is there anyway to ensure that, the function I pass in is a member of certain class? 回答1: Well, if you don't mind

问题 I need make system call from method of Ruby of Rails , but I want it to stay on the same page. Right now for some reason it does not execute , but shows : Routing Error No route matches [POST] "/devices/22918" Try running rake routes for more information on available routes. This is the button: <%= link_to image_tag("/images/glossy_green_button.png"), device , :method => :turnon, :confirm => "Are you sure?" %> This is method: def turnon @device = Device.find(params[:id]) result = `/perl

问题 If I writing a class inside a class, and them both use same methods i.e.: class Master: def calculate(self): variable = 5 return variable class Child: def calculate(self): variable = 5 return variable Do I have to declare this method in both classes, or can I only declare it in the Master, and then use it in Child? 回答1: Nesting one class inside another has no other effect than that the nested class becomes an attribute on the outer class. They have no other relationship. In other words, Child