A class-level security is one in which a caller can call any method of any instance of a class. The declarative security is a class-level security. It is different from an instance-level security in which a caller is allowed to call methods of only a particular instance of a class. Programmatic security is an instance-level security.

The LinkedList class defines the following methods for manipulating lists. These are as follows:

void addFirst(E obj): This method inserts an element at the beginning of the list.
void addLast(E obj): This method inserts an element at the end of a list
>E getFirst(): This method is used to retrieve the first element from the list.
E getLast(): This method retrieves the last element from the list.
E removeFirst(): This removes the first element from the list.
E removeLast(): This method removes the last element from the list.
Here, obj specifies the item.

A constructor provides a convenient way to initialize a newly created object at the time of its creation. It is defined for a class and it is called automatically immediately after the creation of a new object, but before the new operator completes. All Although constructors look the same as methods, they are written by using the following conventions:

1. A constructor is always given the name of the class in which it is defined.
2. A constructor is always written without an explicit return type, not even void. This is because the implicit return type of a class constructor is the class itself.
3. Only accessibility modifiers can be used to declared a constructor. Unlike methods, a constructor cannot be declared as abstract, static, final, native, strictfp, or synchronized.

The FileInputStream class is used to is used to read binary data from a file. It is used to perform simple file input operations. It reads data in a sequential manner, but can skip a region of data as per requirement. It generally reads data in a sequential manner, but can skip a region of data as per requirement. FileInputStream class can be instantiated by using any of the following three constructors:

The package statement is used to declare packages. The word package is a keyword in Java. This statement is not technically needed to write a complete Java program. However, if it appears, it must be the first executable statement in the program. Only comments or white spaces are allowed before a package statement. There can be only one package declaration in a program. If no package declaration appears, the class will belong to the default package.

For example, the following source code file defines a class named ClassA in the package named package4:

package package4;

public class ClassA{
{
// body code
}

This source file will be saved with the name ClassA.java in the directory named package4.

Static methods are those methods that are declared with the keyword static as modifier are called static methods or class methods. It affects a class as a whole, not a particular instance of the class. These methods are always invoked without reference to a particular instance of a class. The static method suffers from the following restrictions:

1. A static method can only call other static methods.
2. A static method must only access static data.
3. A static method cannot reference to the current object using keywords super or this.

An abstract class is a class that is partially implemented. It provides design convenience. An abstract class consists of one or more abstract methods that are declared but left unimplemented. It is the responsibility of subclasses that extend an abstract class to implement the unimplemented part of the abstract class. As the implementation of an abstract class is not complete, it is not possible to directly create objects of an abstract class.

A class containing one or more abstract methods must be declared as abstract. However, a class can also be declared as abstract even if it has no abstract methods. An abstract class may also have non-abstract methods.

Note: The final and abstract class modifiers are not used in combination.

A ClassCastException is thrown when an attempt is made to cast an object, which is not of the appropriate run-time type. It extends from the RuntimeException class. For example:

Object Cst = new Vector();
String s = (String) Cst;

Following are the two kinds of constructors for ClassCastException:
ClassCastException()

It will construct a ClassCastException without any detailed message.
ClassCastException(String str)

It will construct a ClassCastException with the specified detailed message.

BufferedReader: The BufferedReader class extends from the reader class. Its key constructor arguments are Reader.
This class is used for fast reading operations of texts from a character-input stream. It can be used to read single characters, arrays, and lines of data. The size of buffer may or may not be specified. The readLine() method of the BufferedReader class can be used to get the next line of characters from a file, and the skip(long n) method can be used to skip n number of characters.

BufferedWriter: The BufferedWrite class extends from the writer class. This class is used for fast writing operations of texts to a character-output stream. It can be used to write single characters, arrays, and strings of data. The size of buffer may or may not be specified. The BufferedWriter class has the newLine() method that is used to create platform-specific line separators, as some platforms do not support the new line character (‘\n’) to terminate lines.

The Locale class is used to provide a number of convenient constants that are used to create Locale objects for commonly used locales. It is a mechanism for identifying objects, not a container for the objects themselves. The Locale class is used to represent an object that describes a geographical, cultural, or political region. This class is particularly useful for internationalization. Each region has different formats to present the date, time, and numbers. The Locale class is used to present these formats. The Locale class has the following constructors:

• Locale(String language)
  This constructor builds a locale object to represent a language specific to a region.

• Locale(String language, String country)
  This constructor builds a locale object to represent a language specific to a country.

• Locale(String language, String country, String var) This constructor builds a locale object to represent a language specific to a country. The argument var provides the information about the specific vendor or the browser.