can we override start() inside our custom thread class?

Answer 1

yes we can override stat() inside our custom Thread.!!!
proof is the signature of the start() in Thread class
signature is: public void start(){ }
as the method is public we can override it.
example:

class MyThread extends Thread{
public void run(){
for(int i=0; i<=20; i++)
System.out.println("custom Thread: "+i);
}
public void start(){
System.out.println("calling start() of Thread class from start() of MyThread class");
super.start(); //call to Thread class start()
}
public static void main(String[] args){
MyThread mt = new MyThread();
mt.start(); //call to local start() i.e. MyThread
for(int i=0; i<=20; i++)
System.out.println("main Thread: "+i);
}
}

Answer 2

no. override run()