| No. | Method | Description |
|---|---|---|
| 1 | public boolean add(Object element) | is used to insert an element in this collection. |
| 2 | public boolean addAll(collection c) | is used to insert the specified collection elements in the invoking collection. |
| 3 | public boolean remove(Object element) | is used to delete an element from this collection. |
| 4 | public boolean removeAll(Collection c) | is used to delete all the elements of specified collection from the invoking collection. |
| 5 | public boolean retainAll(Collection c) | is used to delete all the elements of invoking collection except the specified collection. |
| 6 | public int size() | return the total number of elements in the collection. |
| 7 | public void clear() | removes the total no of element from the collection. |
| 8 | public boolean contains(object element) | is used to search an element. |
| 9 | public boolean containsAll(Collection c) | is used to search the specified collection in this collection. |
| 10 | public Iterator iterator() | returns an iterator. |
| 11 | public Object[] toArray() | converts collection into array. |
| 12 | public boolean isEmpty() | checks if collection is empty. |
| 13 | public boolean equals(Object element) | matches two collection. |
| 14 | public int hashCode() | returns the hashcode number for collection. |
| Iterator interface provides the facility of iterating the elements in forward direction only. |
| Java Constructor | Java Method |
|---|---|
| Constructor is used to initialize the state of an object. | Method is used to expose behaviour of an object. |
| Constructor must not have return type. | Method must have return type. |
| Constructor is invoked implicitly. | Method is invoked explicitly. |
| The java compiler provides a default constructor if you don't have any constructor. | Method is not provided by compiler in any case. |
| Constructor name must be same as the class name. | Method name may or may not be same as class name. |
abstract class class_name { }
abstract return_type function_name ();
public interface Hockey extends Sports, Event
super.
import java.io.*;class Main { public static void main(String[] args) { FileReader file = new FileReader("C:\\test\\a.txt"); BufferedReader fileInput = new BufferedReader(file); // Print first 3 lines of file "C:\test\a.txt" for (int counter = 0; counter < 3; counter++) System.out.println(fileInput.readLine()); fileInput.close(); }}To fix the above program, we either need to specify list of exceptions using throws, or we need to use try-catch block. We have used throws in the below program. Since FileNotFoundException is a subclass of IOException, we can just specify IOException in the throws list and make the above program compiler-error-free.
Consider the following Java program. It compiles fine, but it throws ArithmeticException when run. The compiler allows it to compile, because ArithmeticException is an unchecked exception.
|
| Instance Variable | Class Variable |
|---|---|
| Instance variables are declared in a class, but outside a method, constructor or any block | Class variables also known as static variables are declared with the static keyword in a class, but outside a method, constructor or a block. |
| Instance variables are created when an object is created with the use of the keyword 'new' and destroyed when the object is destroyed. | Static variables are created when the program starts and destroyed when the program stops. |
| Instance variables can be accessed directly by calling the variable name inside the class. However, within static methods (when instance variables are given accessibility), they should be called using the fully qualified name. ObjectReference.VariableName. | Static variables can be accessed by calling with the class name ClassName.VariableName. |
| Instance variables hold values that must be referenced by more than one method, constructor or block, or essential parts of an object's state that must be present throughout the class. | There would only be one copy of each class variable per class, regardless of how many objects are created from it. |
class ThrowAndThrowsExample
{
void method() throws Exception
{
Exception e = new Exception();
throw e; //throwing an exception using 'throw'
}
}
final can be used to mark a variable "unchangeable"private final String name = "foo"; //the reference name can never change
final can also make a method not "overrideable"
public final String toString() { return "NULL"; }
final can also make a class not "inheritable". i.e. the class can not be subclassed.
public final class finalClass {...}
public class classNotAllowed extends finalClass {...} // Not allowedlock.lock();
try {
//do stuff
} catch (SomeException se) {
//handle se
} finally {
lock.unlock(); //always executed, even if Exception or Error or se
}