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Exam 1 CS-1440 Java Programming
Intro
- The difference between a variable and a literal ANS: A literal is notation for representing a fixed ( const ) value. A variable is storage location associated with a symbolic name (pointed to, if you'd like). In any programming language a Literal is a constant value, where as identifiers can change their values. Identifiers can store literals and process them further.
How to declare a variable ANS: To declare (create) a variable, you will specify the type, leave at least one space, then the name for the variable and end the line with a semicolon ( ; ). Java uses the keyword int for integer, double for a floating point number (a double precision number), and boolean for a Boolean value (true or false).
int score;
How to assign a value to a variable. ANS: Java is pass-by-value. That means pass-by-copy
Declare an int variable and assign it the value '7'. The bit pattern for 7 goes into the variable named x.
int x = 7;
How to initialize a variable. ANS: Initializing a variable. Initializing a variable means specifying an initial value to assign to it (i.e., before it is used at all). Notice that a variable that is not initialized does not have a defined value, hence it cannot be used until it is assigned such a value.
- What a data type is (i.e., what makes up a data type) ANS: A data type is a set of values and a set of operations defined on them. For example, we are familiar with numbers and with operations defined on them such as addition and multiplication. There are eight different built-in types of data in Java, mostly different kinds of numbers. We use the system type for strings of characters so frequently that we also consider it here.
The eight primitive data types, and which ones we are using in this course ANS: Variables and the 8 Primitive Data Types
The Purpose of a Variable (and some vocabulary)
You can think of a simple program as a list of instructions to be read and acted upon sequentially
Example:
Read a value representing the radius of a circle from the standard input source/stream
Compute the area of a circle with this radius
Print the area to the standard output stream (i.e., the console window)
Remember: a computer will read and act upon these instructions one at a time ANS: it is not aware of what is coming up until it gets there!
Looking at step 1 in the program above, we will need to tell the computer that it needs to remember the value it is reading in ANS: it needs to store this value in its memory somewhere so we can use it in a computation later.
We need to tell the computer how much memory will be needed to store the value in question. Different kinds of numbers require different amounts of memory (more on this in a minute). Of course, we sometimes need to store things other than numbers. These things too, come in different sizes. For example, it will certainly take more memory to store the Declaration of Independence than it will to store a single letter (i.e., a "character"). Further, we also need to tell the computer how the value should be stored in memory (i.e., what method of "encoding" should be employed to turn the value into a string of 1's and 0's). Examples of types of encodings used include Two's Complement, IEEE 754 Form, ASCII, Unicode, etc...
The computer also needs to have some reference to where it stored the value, so it can find it again.
The concept of a variable solves all of our problems here. A variable in Java gives us a way to store values (or other kinds of information) for later use, addressing all of the aforementioned considerations.
System.out.println(" i = " + i);
System.out.println(" j = " + j);
System.out.println(" x = " + x);
System.out.println(" y = " + y);
//adding numbers
System.out.println("Adding...");
System.out.println(" i + j = " + (i + j));
System.out.println(" x + y = " + (x + y));
//subtracting numbers
System.out.println("Subtracting...");
System.out.println(" i ANS: j = " + (i ANS: j));
System.out.println(" x ANS: y = " + (x ANS: y));
//multiplying numbers
System.out.println("Multiplying...");
System.out.println(" i * j = " + (i * j));
System.out.println(" x * y = " + (x * y));
//dividing numbers
System.out.println("Dividing...");
System.out.println(" i / j = " + (i / j));
System.out.println(" x / y = " + (x / y));
//computing the remainder
Understand operator precedence and associativity ANS: Associativity is used when two operators of same precedence appear in an expression. Associativity can be either Left to Right or Right to Left. For example '*' and '/' have same precedence and their associativity is Left to Right, so the expression "100 / 10 * 10" is treated as "(100 / 10) * 10".
How to use a combined assignment operator ANS: Variables and Combined Assignment Operators
You'll commonly want to complete a math function and assign the resulting value back to some named object, called a variable. ActionScript makes this easier by letting you combine arithmetic and assignment operators together. Take a look at an assignment operator example:
Create a new ActionScript 3.0 project and enter in the following code for the project:
// Assignment Operators
var myValue:Number = 2;
myValue = myValue + 2;
trace(myValue);
var myOtherValue:Number = 2;
myOtherValue += 2;
trace(myOtherValue);
Run the project. You'll get the following in the Output panel:
4
4
Let's walk through the code and explain how you get this result and what role variables and combined assignment operators play.
Variables
Widening a smaller primitive value to a bigger primitive type.
class A
{
public static void main(String... ar)
{
byte b=10;
short s= b; //byte value is widened to short
int i=b; //byte value is widened to int
long l=b; //byte value is widened to long
float f=b; //byte value is widened to float
double d=b; //byte value is widened to double
System.out.println("short value : "+ s);
System.out.println("int value : "+ i);
System.out.println("long value : "+ l);
System.out.println("float value : "+ f);
System.out.println("double value : "+ d);
}
Output-
short value : 10
int value : 10
long value : 10
float value : 10.
double value : 10.
In the preceding code, we have widened a smaller byte value to several bigger primitive values like byte, short, int, long and float.
Widening a subclass object reference to a wider superclass object reference.
This is also known as upcasting the subclass reference to its superclass reference.
class A
{
public void message()
{
System.out.println("message from A");
}
}
In these situations, you can use a process called casting to convert a value from one type to another. Although casting is reasonably simple, the process is complicated by the fact that Java has both primitive types (such as int, float, and boolean) and object types (String, Point, and the like).
- How to create a named constant. ANS: Name an array constant
Click Formulas > Define Name.
In the Name box, enter a name for your constant.
In the Refers to box, enter your constant. ...
Click OK.
In your worksheet, select the cells that will contain your constant.
In the formula bar, enter an equal sign and the name of the constant, such as =Quarter1.
Press Ctrl+Shift+Enter.
What a reference variable is ANS: A reference variable is an alias, that is, another name for an already existing variable. Once a reference is initialized with a variable, either the variable name or the reference name may be used to refer to the variable.
How to declare a variable of type String. ANS: Ask Question
This question already has an answer here:
What are classes, references and objects? 9 answers
class Demo
{
String title;
private int num;
}
String is a class, so when we declare title, is that treated as object or just a variable? I know this is a very basic thing, but i need help. Thanks in advance.
How to read keyboard input from the user. ANS: Input from Keyboard
The input Function
Input via keyboard There are hardly any programs without any input. Input can come in various ways, for example from a database, another computer, mouse clicks and movements or from the internet. Yet, in most cases the input stems from the keyboard. For this purpose, Python provides the function input(). input has an optional parameter, which is the prompt string.
If the input function is called, the program flow will be stopped until the user has given an input and has ended the input with the return key. The text of the optional parameter, i.e. the prompt, will be printed on the screen.
The input of the user will be interpreted. If the user e.g. puts in an integer value, the input function returns this integer value. If the user on the other hand inputs a list, the function will return a list.
Let's have a look at the following example:
name = input("What's your name? ")
print("Nice to meet you " + name + "!")
age = input("Your age? ")
print("So, you are already " + str(age) + " years old, " + name + "!")
We save the program as "input_test.py" and run it:
$ python input_test.py
Left-justifying printf integer output
The printf integer zero-fill option
printf integer formatting
formatting floating point numbers with printf
printf string formatting
printf special characters
Related printf content
Summary: This page is a printf formatting cheat sheet. I originally created this cheat sheet for my own purposes, and then thought I would share it here.
A great thing about the printf formatting syntax is that the format specifiers you can use are very similar — if not identical — between different languages, including C, C++, Java, Perl, PHP, Ruby, Scala, and others. This means that your printf knowledge is reusable, which is a good thing.
printf formatting with Perl and Java
In this cheat sheet I'll show all the examples using Perl, but at first it might help to see one example using both Perl and Java. Therefore, here's a simple Perl printf example to get things started:
printf("the %s jumped over the %s, %d times", "cow", "moon", 2);
And here are three different Java printf examples, using different string formatting methods that are available to you in the Java programming language:
System.out.format("the %s jumped over the %s, %d times", "cow", "moon", 2);
System.err.format("the %s jumped over the %s, %d times", "cow", "moon", 2);
String result = String.format("the %s jumped over the %s, %d times", "cow", "moon", 2);
As you can see in that last String.format example, that line of code doesn't print any output, while the first line prints to standard output, and the second line prints to standard error.
In the remainder of this document I'll use Perl examples, but ag
How to use String.format to nicely format strings. ANS: The most common way of formatting a string in java is using String.format(). If there were a "java sprintf" then this would be it. String output = String.format("%s = %d", "joe", 35); For formatted console output, you can use printf() or the format() method of System.out and System.err PrintStreams.
Our style conventions for naming program entities, including comments in our
programs, and formatting our programs. ANS: Google Python Style Guide
1 Background
Python is the main dynamic language used at Google. This style guide is a list of dos and don'ts for Python programs.
To help you format code correctly, we've created a settings file for Vim. For Emacs, the default settings should be fine.
Many teams use the yapf auto-formatter to avoid arguing over formatting.
2 Python Language Rules
2.1 Lint
Run pylint over your code.
Suppressing in this way has the advantage that we can easily search for suppressions and revisit them.
You can get a list of pylint warnings by doing:
pylint --list-msgs
To get more information on a particular message, use:
pylint --help-msg=C
Prefer pylint: disable to the deprecated older form pylint: disable-msg.
Unused argument warnings can be suppressed by deleting the variables at the
What a class definition is and how to write one ANS: How to define class in Python?
The key concept in this programming paradigm is classes. In Python, these are used to create objects which can have attributes. Objects are specific instances of a class. A class is essentially a blueprint of what an object is and how it should behave.
How a class can be considered a "smart data type" ANS: Rational Software Architect 8.5.x: new features and enhancements
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Abstract
This document provides an overview of new features and enhancments in IBM Rational Software Architect version 8.5 releases.
Content
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9.0 Release 8.5.5 Fix Pack 4 8.5.5 Fix Pack 3 8.5.5 Fix Pack 2 8.5.5 Fix Pack 1 8.5 Fix Pack 5 8.5 Mod Pack 1 8.5. Release
Rational Software Architect, Version 8.5.5.
Link Date Released Status
Download 8.5.5.4 Release 11/20/2015 Current
This release of Rational Software Architect contains new features and enhancements in the following areas:
IBM product integration support IBM Runtime Environment Java Technology Edition updates Eclipse platform updates
Product integration support
The following product integration is supported beginning with v8.5.5.4:
Rational Common Licensing 8.1.4.
IBM Installation Manager 1.8.
Rational Team Concert 5.0.2 and 6.
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IBM Runtime Environment Java Technology Edition updates
IBM Runtime Environment Java Technology Edition is updated to the following versions:
IBM 32/64-bit Runtime Environment for Windows, Java Technology Edition, Version 7.0 Service Release 9 FP
IBM 32/64-bit Runtime Environment for Linux, Java Technology Edition, Version 7.0 Service Release 9 FP
Public
access-modifiers-in-java
Default: When no access modifier is specified for a class , method or data member ANS: It is said to be having the default access modifier by default.
The data members, class or methods which are not declared using any access modifiers i.e. having default access modifier are accessible only within the same package.
In this example, we will create two packages and the classes in the packages will be having the default access modifiers and we will try to access a class from one package from a class of second package.
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//Java program to illustrate default modifier
package p1;
//Class Geeks is having Default access modifier
class Geek
{
void display()
{
System.out.println("Hello World!");
}
}
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//Java program to illustrate error while
//using class from different package with
//default modifier
package p2;
import p1.*;
//This class is having default access modifier
class GeekNew
{
public static void main(String args[])
{
//accessing class Geek from package p
Geeks obj = new Geek();
obj.display();
}
}
Output:
