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Object methods

public native int hashCode();
public boolean equals(Object obj) {
  return (this == obj);
protected native Object clone() throws CloneNotSupportedException;
public String toString() {
  return getClass().getName() + "@" + Integer.toHexString(hashCode());
public final native void notify();
public final native void notifyAll();
public final native void wait(long timeout) throws InterruptedException;
protected void finalize() throws Throwable { }

ob1.Equals(ob2) --> ob1.hashcode == ob2.hashcode


Java collection faq

Map is not a collection.


  1. differences between ArrayList and LinkedList
  2. HashMap
  3. BinaryTree

Interfaces, Classess:



wait, notify, notifyAll, concurrent

syncronized, volatile


There are 4 main components: activity, service, broadcastreceiver, ContentProvider

BroadcastReceiver can be registered in manifest or in code.

Service lifecycle:

Restart of service:

Service in UI and service in another thread

Activity lifecycle:

if a view has ID then


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