5th Six Weeks

Question 0

this

Answer 0

Within an instance method or a constructor, this is a reference to the current object — the object whose method or constructor is being called. You can refer to any member of the current object from within an instance method or a constructor by using this. The most common reason for using the this keyword is because a field is shadowed by a method or constructor parameter. From within a constructor, you can also use the this keyword to call another constructor in the same class. Doing so is called an explicit constructor invocation.

Question 1

interface

Answer 1

In the Java programming language, an interface is a reference type, similar to a class, that can contain only constants, method signatures, default methods, static methods, and nested types. Method bodies exist only for default methods and static methods. Interfaces cannot be instantiated—they can only be implemented by classes or extended by other interfaces.

Question 2

abstract class

Answer 2

An abstract class is a class that is declared abstract—it may or may not include abstract methods. Abstract classes cannot be instantiated, but they can be subclassed.

Question 4

abstract method

Answer 4

An abstract method is a method that is declared without an implementation (without braces, and followed by a semicolon)

Question 5

How is an abstract class similar to an interface?

Answer 5

Abstract classes are similar to interfaces. You cannot instantiate them, and they may contain a mix of methods declared with or without an implementation. However, with abstract classes, you can declare fields that are not static and final, and define public, protected, and private concrete methods. With interfaces, all fields are automatically public, static, and final, and all methods that you declare or define (as default methods) are public. In addition, you can extend only one class, whether or not it is abstract, whereas you can implement any number of interfaces.

Question 6

final

Answer 6

You can declare some or all of a class’s methods final. You use the final keyword in a method declaration to indicate that the method cannot be overridden by subclasses. The Object class does this—a number of its methods are final. You might wish to make a method final if it has an implementation that should not be changed and it is critical to the consistent state of the object.

Question 7

Data Structures

Answer 7

In computer science, a data structure is a particular way of organizing data in a computer so that it can be used efficiently.

Question 8

Foreach loop

Answer 8

For each (or foreach) is a computer language idiom for traversing items in a collection. Foreach is usually used in place of a standard for statement. Unlike other for loop constructs, however, foreach loops[1][2] usually maintain no explicit counter: they essentially say “do this to everything in this set”, rather than “do this x times”. This avoids potential off-by-one errors and makes code simpler to read. In object-oriented languages an iterator, even if implicit, is often used as the means of traversal.

Question 9

abs() method

Answer 9

The method gives the absolute value of the argument. The argument can be int, float, long, double, short, byte.

Question 10

lastIndexOf()

Answer 10

int lastIndexOf(int ch): Returns the index within this string of the last occurrence of the specified character or -1 if the character does not occur.

public int lastIndexOf(int ch, int fromIndex): Returns the index of the last occurrence of the character in the character sequence represented by this object that is less than or equal to fromIndex, or -1 if the character does not occur before that point.

public int lastIndexOf(String str): If the string argument occurs one or more times as a substring within this object, then it returns the index of the first character of the last such substring is returned. If it does not occur as a substring, -1 is returned.

public int lastIndexOf(String str, int fromIndex): Returns the index within this string of the last occurrence of the specified substring, searching backward starting at the specified index.