What’s the accepted procedure and paths to configure jdk and global library source code for Intellij IDEA on OS X?

Answer

As of the latest releases:

• Java for Mac OS X 10.6 Update 3
• Java for Mac OS X 10.5 Update 8

Apple has moved things around a bit.

To quote the Apple Java guy on the java-dev mailing list:

1. System JVMs live under /System/Library/…

   • These JVMs are only provided by Apple, and there is only 1 major
     platform version at a time.
   • The one version is always upgraded, and only by Apple Software Updates.
   • It should always be GM version, that developers can revert back to, despite
     any developer previews or 3rd party
     JVMs they have installed.
   • Like everything else in /System, it’s owned by root r-x, so don’t mess
     with it!

2. Developer JVMs live under /Library/Java/JavaVirtualMachines

   • Apple Java Developer Previews install under /Library.
   • The Developer .jdk bundles contain everything a developer could need
     (src.jar, docs.jar, etc), but are too
     big to ship to the tens of millions of
     Mac customers.
   • 3rd party JVMs should install here.

3. Developers working on the JVM itself can use
   ~/Library/Java/JavaVirtualMachines

   • It’s handy to symlink to your current build product from this
     directory, and not impact other users

4. Java IDEs should probably bias to using /Library or ~/Library detected
   JVMs, but should be able to fallback
   to using /System/Library JVMs if
   that’s the only one installed (but
   don’t expect src or JavaDoc).

This allows Java developers the
maximum flexibility to install
multiple version of the JVM to regress
bugs and even develop a JVM on the Mac
themselves. It also ensures that all
Mac customers have one safe, slim,
secure version of the JVM, and that we
don’t endlessly eat their disk space
every time we Software Update them a
JVM.

So, instead of pointing Intellij at /System/Library/Frameworks/JavaVM.framework, you should point to a JDK in either /Library/Java/JavaVirtualMachines or /System/Library/Java/JavaVirtualMachines

In plain Java SE 6 environment:

Logger l = Logger.getLogger("nameless");
l.setLevel(Level.ALL);
l.fine("somemessage");

Nothing shows up in Eclipse console. l.info(“”) and above works just fine, but anything below fine just doesn’t seem to work. What’s could be wrong? TIA.

Answer

Even though the Logger level is set to ALL, the ConsoleHandler (the default Handler on the logger) still has a default level of INFO. This comes from the default logging.properties in JAVA_HOME/jre/lib

What’s the explanation for the following:

public class GenericsTest {
    //statement 1
    public ArrayList<Integer>[] lists;

    public GenericsTest()
    {
            //statement 2
        lists = new ArrayList<Integer>[4];
    }
}

The compiler accepts statement 1. Statement 2 is flagged by the compiler for “generic array creation”.

A good explanation I’ve seen regarding disallowing generic arrays is this one, arguing that since arrays are covariant and generics are not you could subvert the generic typing if you allowed generic arrays.

Leaving aside the argument over whether the language should go to the extreme lengths of creating this kind of complicated inconsistency in the treatment of generics to keep you from shooting yourself no matter how hard you try (and if anyone knows of any good discussions on the relative merits/demerits of the issue please post, I’d be interested to see the arguments), why should statement (1) be allowed if (2) isn’t?

Answer

There seems to be obscure cases where you could inadvertently cause a ClassCastException as explained here http://java.sun.com/j2se/1.5/pdf/generics-tutorial.pdf (section 7.3)

an intersting discussion on this topic could be found here http://courses.csail.mit.edu/6.170/old-www/2006-Spring/forum/index.php%3Ftopic=324.msg1131.html

How can I use RMI with a applet client behind a firewall?

How can I use RMI with a firewalled server and firewalled applet client? (If possible)

I know that the RMI server uses port 1099 (by default, but this is configurable); however after this the communication requires a new socket on a different random port. I also know that you can set the proxy on the client for RMI over HTTP tunneling which in theory should solve my issue. But I can’t make it work (I tried setting the environmental properties on my XP client, but Internet Explorer keeps ignoring them).

Answer

See http://java.sun.com/javase/6/docs/technotes/guides/rmi/faq.html#firewall

Is there a quick way to set an HTML text input (<input type=text />) to only allow numeric keystrokes (plus ‘.’)?

Answer

^{Note: This is an updated answer. Comments below refer to an old version which messed around with keycodes.}

JavaScript

Try it yourself on JSFiddle.

You can filter the input values of a text <input> with the following setInputFilter function (supports Copy+Paste, Drag+Drop, keyboard shortcuts, context menu operations, non-typeable keys, the caret position, different keyboard layouts, and all browsers since IE 9):

// Restricts input for the given textbox to the given inputFilter function.
function setInputFilter(textbox, inputFilter) {
  ["input", "keydown", "keyup", "mousedown", "mouseup", "select", "contextmenu", "drop"].forEach(function(event) {
    textbox.addEventListener(event, function() {
      if (inputFilter(this.value)) {
        this.oldValue = this.value;
        this.oldSelectionStart = this.selectionStart;
        this.oldSelectionEnd = this.selectionEnd;
      } else if (this.hasOwnProperty("oldValue")) {
        this.value = this.oldValue;
        this.setSelectionRange(this.oldSelectionStart, this.oldSelectionEnd);
      } else {
        this.value = "";
      }
    });
  });
}

You can now use the setInputFilter function to install an input filter:

setInputFilter(document.getElementById("myTextBox"), function(value) {
  return /^d*.?d*$/.test(value); // Allow digits and '.' only, using a RegExp
});

See the JSFiddle demo for more input filter examples. Also note that you still must do server side validation!

TypeScript

Here is a TypeScript version of this.

function setInputFilter(textbox: Element, inputFilter: (value: string) => boolean): void {
    ["input", "keydown", "keyup", "mousedown", "mouseup", "select", "contextmenu", "drop"].forEach(function(event) {
        textbox.addEventListener(event, function(this: (HTMLInputElement | HTMLTextAreaElement) & {oldValue: string; oldSelectionStart: number | null, oldSelectionEnd: number | null}) {
            if (inputFilter(this.value)) {
                this.oldValue = this.value;
                this.oldSelectionStart = this.selectionStart;
                this.oldSelectionEnd = this.selectionEnd;
            } else if (Object.prototype.hasOwnProperty.call(this, 'oldValue')) {
                this.value = this.oldValue;
                if (this.oldSelectionStart !== null &&
                    this.oldSelectionEnd !== null) {
                    this.setSelectionRange(this.oldSelectionStart, this.oldSelectionEnd);
                }
            } else {
                this.value = "";
            }
        });
    });
}

jQuery

There is also a jQuery version of this. See this answer.

HTML 5

HTML 5 has a native solution with <input type="number"> (see the specification), but note that browser support varies:

• Most browsers will only validate the input when submitting the form, and not when typing.
• Most mobile browsers don’t support the step, min and max attributes.
• Chrome (version 71.0.3578.98) still allows the user to enter the characters e and E into the field. Also see this question.
• Firefox (version 64.0) and Edge (EdgeHTML version 17.17134) still allow the user to enter any text into the field.

Try it yourself on w3schools.com.