John Vilk

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[] + [] // = "" (empty string)
[] + {} // = the string "[object Object]"
"hello" + 1 // = the string "hello1"
"hello" - 1 // = NaN (not a number)
'3' == 3 // true; implicitly converts 3 to '3'
'3' === 3 // false
3 === 3 // true
var someObject = {
  // number
  foo: 3,
  // array
  bar: [1, 2, 3],
  baz: '3'
};
someObject.foo; // 3
someObject['foo']; // 3
someObject.newProperty = "hello"; // Creates a new object property
var someObject = {};
var someObjectPrototype =  {
  foo: 3
};
Object.setPrototypeOf(someObject, someObjectPrototype);
// Inherited field from prototype
someObject.foo; // 3
// Creates field foo on someObject, distinct from prototype's
// foo field!
someObject.foo = 4;
someObject.foo; // 4
someObjectPrototype.foo; // 3
var arr = ["hello"];

// You can add properties to arrays, like objects.
arr.newProperty = 3;

typeof(arr); // "object"
function Dog(name) {
  // 'this' points to the new Dog object you're constructing.
  this.name = name;
  this.animalType = "dog";
  this.sound = "woof";
}
// All Dog objects will have the prototype Dog.prototype,
// and thus will have the function getSound().
Dog.prototype.getSound = function() {
  return this.sound;
}

var charles = new Dog('Charles');
charles.getSound(); // 'woof'
charles instanceof Dog; // true
charles instanceof Object; //true
// Change Dog's prototype object.
Dog.prototype = Object;
// charles's prototype object is no longer
// equal to Dog.prototype, so instanceof returns
// false.
charles instanceof Dog; // false
var buttons = document.getElementsByTagName('button');
// Assumption: There's only one button on the page.
var button = buttons[0];
var clicked = false;
button.addEventListener('click', function() {
  clicked = true;
});
// Check if user clicked button after 5 seconds
// via a timer event.
setTimeout(function() {
  if (clicked) {
    alert("You clicked the button! :D");
  } else {
    alert("You didn't click the button. :(")
  }
}, 5000);
<!doctype html>
<html>
<script type="text/javascript">
// Wrap in timer so button displays before
// we crash the tab.
setTimeout(function() {
  while (1) {
    // Infinite loop. :D
  }
}, 100);
</script>
<button>Try to click me. You can't.</button>

</html>
var error = false;
function bar() {
  if (error) {
    // If you have developer tools open, the debugger statement triggers a breakpoint.
    debugger;
    alert("Error occurred!");
  }
}

function foo() {
  bar();
}

function baz() {
  error = true;
}

// Run baz after 50 milliseconds
setTimeout(baz, 50);
// Run foo after 5 seconds.
setTimeout(foo, 5000);
var data;
var button = document.getElementsByTagName('button')[0];
button.addEventListener('click', function() {
  alert(data);
});
setTimeout(function() {
  data = "Welcome to this website!";
}, 2000);
<style type="text/css">
@keyframes color_change {
  from { background-color: blue; }
  to { background-color: red; }
}
#picker { animation: color_change 5s infinite alternate; }
</style>
<div id="picker">
  Picker
</div>
<script type="text/javascript">
// Checks if element e has a blue background.
function isBlue(e) {
  var color = getComputedStyle(e).backgroundColor;
  return color === 'rgb(0, 0, 255)';
}

var div = document.getElementById('picker');
if (isBlue(div)) {
  // do something
}

// Observe that the animation continues when the program
// is paused at this breakpoint!
debugger;

if (isBlue(div)) {
  // do something
}

</script>
$ java example/CowboyArtist
Exception in thread "main" java.lang.IncompatibleClassChangeError: Conflicting default methods: example/Cowboy.draw example/Painter.draw
at example.CowboyArtist.draw(CowboyArtist.java)
at example.CowboyArtist.main(CowboyArtist.java:6)

// In example/Cowboy.java:
package example;

public interface Cowboy {
}

// In example/Painter.java:
package example;

public interface Painter {
  default void draw() {
    System.out.println("Here's a picture...");
  }
}

// In example/CowboyArtist.java:
package example;
import example.*;

public class CowboyArtist implements Cowboy, Painter {
  public static void main(String[] args) {
    new CowboyArtist().draw();
  }
}
$ javac example/CowboyArtist.java
$ java example.CowboyArtist
Here's a picture...

package example;

public interface Cowboy {
  default void draw() {
    System.out.println("Bang!");
  }
}
$ javac example/Cowboy.java
$ java example.CowboyArtist
Exception in thread "main" java.lang.IncompatibleClassChangeError: Conflicting default methods: example/Cowboy.draw example/Painter.draw
at example.CowboyArtist.draw(CowboyArtist.java)
at example.CowboyArtist.main(CowboyArtist.java:6)

public class Test {
  public static void main(String[] args) {
    new Dog().makeNoise(); // Prints "Bark!"
  }
}
interface Animal {
  public String getNoise();
  default void makeNoise() {
    System.out.println(this.getNoise());
  }
}
class Dog implements Animal {
  public String getNoise() {
    return "Bark!";
  }
}
public class JavaCHatesMe implements IFace1, IFace2 {

}
interface IFace1 {
  default void foo() {}
}
interface IFace2 {
  default void foo() {}
}
$ javac JavaCHatesMe.java
JavaCHatesMe.java:1: error: class JavaCHatesMe inherits unrelated defaults for foo() from types IFace1 and IFace2
public class JavaCHatesMe implements IFace1, IFace2 {
  ^
  1 error

public class WTF {
  public static void main(String[] args) {
    ISpeak.test();
  }
}

interface ISpeak {
  default void speak() {
    System.out.println("ISpeak Speaking!");
  }

  public static void test() {
    new EmptySpeakImpl().speak();
    new EmptySpeakImplChild().speak();
  }
}

interface ISpeak2 extends ISpeak {
  default void speak() {
    System.out.println("ISpeak2 Speaking!");
  }
}

class EmptySpeakImpl implements ISpeak2 {}
class EmptySpeakImplChild extends EmptySpeakImpl implements ISpeak {}
$ java WTF
ISpeak2 Speaking!
ISpeak2 Speaking!

John Vilk

Penn PL Club Homework: Making the Browser Reasonable for Sane Programmers

Basic JavaScript

Event-driven Execution

Events and Debugging

Race Conditions

Event Scheduling

Browser Components

Conclusion

Java 8 Specification Bug: Default Interface Method Resolution

Email to the JLS/JVM Committee

Replicating the Behavior

Life Lessons Learned

Java 8 WTF: Ambiguous Method Lookup

Introduction to Default Interface Methods

JVM Changes Required

Multiple Inheritance Troubles

Taking a Look at the JVM Specification

Edit: Alternative JVM Specification Interpretation

Edit 2: A little more complication…

Next Post: `invokedynamic`

New Website Launch

Enter Jekyll

Starting a blog?!

Feedback

John Vilk

Penn PL Club Homework: Making the Browser Reasonable for Sane Programmers

Basic JavaScript

Event-driven Execution

Events and Debugging

Race Conditions

Event Scheduling

Browser Components

Conclusion

Java 8 Specification Bug: Default Interface Method Resolution

Email to the JLS/JVM Committee

Replicating the Behavior

Life Lessons Learned

Java 8 WTF: Ambiguous Method Lookup

Introduction to Default Interface Methods

JVM Changes Required

Multiple Inheritance Troubles

Taking a Look at the JVM Specification

Edit: Alternative JVM Specification Interpretation

Edit 2: A little more complication…

Next Post: invokedynamic

New Website Launch

Enter Jekyll

Starting a blog?!

Feedback

Next Post: `invokedynamic`