1.
Set val = new TreeSet();
val.add("6");
val.add(7);
With warning and throw below Exception when run.
java.lang.ClassCastException: java.lang.String incompatible with java.lang.Integer
2. public class FileReader extends InputStreamReader
3. Order
static {System.out.println("111");}
{System.out.println("222");}
public constuctor() {
System.out.println("333");
}