Why wait ,notify and notifyAll Methods are in Object Class?

Question

i know that wait() method always written in synchronized method/block and make lock on Object but i want to only know that what problem is arise at that time when this all m

Answer 1

These method's context is a lock associated with every object in Java so we can't move them to the Thread class. For example we might do something like this. Thread 1 adds an item to a list and notifies other threads about it. Thread 2 waits for a list update and does something with it:

thread 1
synchronized (lock) {
    list.add(item);
    lock.notifyAll();     
}

thred 2 
synchronized (lock) {
    list.wait();
    ... do something with list
}

If these methods were moved to a thread, the thing we done here would be impossible.