Answer Posted / aravinda reddy

ArrayList is by default not thread safe, but we can make it
thread safe. Below is the example how we can make it thread
safe.

public class SynchronizeList {
public static void main(String[] args) {

ArrayList<String> al=new ArrayList<String>
();
al.add("1");
al.add("2");
al.add("3");

//we can make the synchronized
Collections.synchronizedList(al);

synchronized(al) {
Iterator i = al.iterator(); // Must
be in synchronized block
while (i.hasNext())
System.out.println(i.next());
}
}
}

Vector and HashTable are by default synchronized. These are
thread safe.

Hence the answer is ArrayList.

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