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doc & reference Edit

SingletonEdit

static synchronized methodEdit

  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 Edit

Java 5 new features Edit

Generics Edit

  • 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 Edit

  • 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 Edit

  • auto conversion between primitives and wrappers

Type safe Enums Edit

  • Enums are type safe.
  • Enums are Serializable and Comparable by default
  • Programmers doesn’t require to do extra work of implementing toString(), equals() and hashCode(). Enums provide implementation of these by default.
  • Programmers can use Enums in switch-case statements.
  • Enums are permitted to implement to interfaces.

old style:

public class Dialog {
    public static final int SHORT = 0;
    public static final int LONG = 1;
    public static void show(int duration) {
        if(duration == SHORT) ...
        else if (duration == LONG) ...
    }
    ....
    Dialog.show(Dialog.LONG);
}

new style:

public class Dialog {
    public enum Duration {LONG, SHORT};
    public static void show(Duration e) {
        if (e == Duration.SHORT) ...
        else if (e == Duration.Long) ...
    }
...
Dialog.show(Duration.Long);
 
}


Varargs Edit

  • Variable size argument lists for method
void orderCar(int modelNo, String... options) {}
 
orderCar(Benz.E_CLASS, "navigation", "hi pass");
public void foo(int i, String... strings) {
    	  String[] someStrings = strings;
    	  // rest of method body
}

Annotation (metadata) Edit

  • attach extra information about code
    • compiler check
    • code analysis
@Override
public boolean equals(Object obj)
 
 
@Deprecated
public doSomething() ...
 
 
@SuppressWarnings("deprecation")
public static void selfDestruct() {
    Thread.currentThread().stop();
}

static import Edit

  • avoiding qualifying static members

formated output Edit

  • printf(), String.format();
System.out.printf("Hello %s %s, "world", "hi");
String s = String.format("The meaning of %s", "right");

a Iterator with predicate Edit

  • FilterIterator in commons cllection

https://github.com/yren/java-basic/blob/master/src/main/java/com/lokvin/basic/FilterIterator.java

java finalize method Edit

java enum Edit

java annotation Edit

java reflection & introspection Edit

Decorator design pattern Edit

java anonymous inner class Edit

apache commons beanutils Edit

apache commons langEdit

java performance Edit

java default char encoding Edit

arrow operation, lambda Edit

java8 features Edit