Govt. Exams
Entrance Exams
List list = new ArrayList();
list.add("Hello");
List raw = list; // Unchecked assignment
raw.add(123); // Adding Integer to raw type
String s = list.get(1);
Raw type assignment bypasses generics. Integer 123 is added to the list. When casting to String at get(1), ClassCastException occurs.
ArrayList<Integer> is a subtype of List<Integer> because ArrayList is a subclass of List with the same type parameter.
public T getMax(T a, T b) {
return a.compareTo(b) > 0 ? a : b;
}
What is the benefit of this recursive bound ?
Recursive bound <T extends Comparable<T>> ensures that T implements Comparable interface specifically for comparing with its own type, providing type safety.
List list = new ArrayList();
list.add(123); // Adding Integer
String s = (String) list.get(0);
Raw type List accepts any object. At runtime, the Integer 123 cannot be cast to String, causing ClassCastException.
PECS principle: use 'extends' when reading from a collection (source), use 'super' when writing to it (dest). Option A reads from source and writes to dest correctly.
getMetaData() on ResultSet returns ResultSetMetaData which provides column information. getColumnCount() and getColumnName() are methods of ResultSetMetaData used to retrieve structure details.
DataSource with connection pooling frameworks (HikariCP, C3P0) efficiently manages connections by reusing them, reducing overhead. Direct getConnection() calls create new connections each time, which is inefficient for high concurrency.
executeBatch() behavior on failure varies by database and driver. BatchUpdateException is thrown, containing update counts for each statement. Explicit transaction control is recommended.
If query execution itself is slow (5 seconds), the bottleneck is in database operations, not data transfer. Increasing setFetchSize() only optimizes data retrieval, not query execution.
CallableStatement is specifically designed for stored procedures, supporting registerOutParameter() for output parameters and getMoreResults() for multiple result sets.
