Java

doc & reference

• http://howtodoinjava.com/ - how to do in java. A very good guy who share lots of his experience
• http://www.mkyong.com/ - Another site which you can find java dev experience
• http://www.careercup.com/ - career cup. A site you can find interview questions.

Singleton

• http://www.infoq.com/cn/articles/double-checked-locking-with-delay-initialization - singleton double check locking and lazy initialize
• http://en.wikipedia.org/wiki/Singleton_pattern#Lazy_initialization

static synchronized method

1. difference between static synchronized method and non-static synchronized method

• The lock objects are difference between static synchronized method and non-static synchronized method. Static synchronized method lock object is class object (lock object: FooClass.class), non-static synchronized lock object is instance object (lock object: this).

   public class Foo {
           public static synchronized void methodA() {}

           public synchronized void methodB() {}
   }

It's roughly equals

public class Foo {
  public static void methodA() {
    synchronized(Foo.class) {
        ...
    }
  }

  public void methodB() {
      synchronized(this){
      
      } 

  }
}

HashMap

• http://howtodoinjava.com/2012/10/09/how-hashmap-works-in-java/ - how HashMap work in java
• http://howtodoinjava.com/2012/10/09/working-with-hashcode-and-equals-methods-in-java/ - working with equals(), hashCode() in java

Java 5 new features

Generics

• Add compile time type safe
• Elimination drudgery class casting

old style:

List list = new ArrayList();
...
String s = (String)list.get(0);

---

new style:

List<String> list = new ArrayList<String>();
...
String s = list.get(0);

Enhance for Loop

• The new enhanced for loop provides a simple, consistent syntax for iterating over collections and arrays.

old style:

String[] arr = new String[]{"alpha", "beta"};
for (int i=0; i<=arr.length; i++) {
    String t = arr[i];
    System.out.println(t);
}

new style:

String[] arr = new String[]{"alpha", "beta"};
for (String s : arr) {
    System.out.println(s);
}

• some limitation of enhance loop, some time we need index and iterator

example need index:

for (int i=0; i<numbers.length; i++) {
  if (i !=0 && i != numbers.length - 1) {
        System.out.println(",");
  }
  System.out.println(numbers[i]);
}

example need iterator:

for (Iterator<String> it = n.iterator(); it.hasNext(); ) {
    if (it.next() < 0) it.remove();

}

Auto Boxing/ Auto un-boxing

• auto conversion between primitives and wrappers