Programming Errors in Java language

             Lesson 8:            

Programming errors can be categorized into three types (3): 

1. SYNTAX ERROR

2. RUNTIME ERROR

3. LOGIC ERRORS.

1. Syntax Errors

Errors that are detected by the compiler are called syntax errors or compile errors. Syntax errors result from errors in code construction, such as mistyping a keyword, omitting some necessary punctuation, or using an opening brace without a corresponding closing brace. These errors are usually easy to detect because the compiler tells you where they are and what caused them. For example, in listing 1.4 as shown in Figure 1.10 below.

Four errors are reported, but the program actually has two errors:

■ The keyword void is missing before main in line 2.

■ The string Welcome to Java should be closed with a closing quotation mark in line 3.

Since a single error will often display many lines of compile errors, it is a good practice to fix errors from the top line and work downward. Fixing errors that occur earlier in the program may also fix additional errors that occur later.

Tip

If you don’t know how to correct it, compare your program closely, character by character, with similar examples in the text. In the first few weeks of this course, you will probably spend a lot of time fixing syntax errors. Soon you will be familiar with Java syntax and can quickly fix syntax errors.

2. Runtime Errors

Runtime errors are errors that cause a program to terminate abnormally. They occur while a program is running if the environment detects an operation that is impossible to carry out. Input mistakes typically cause runtime errors. An input error occurs when the program is waiting for the user to enter a value, but the user enters a value that the program cannot handle.

For instance, if the program expects to read in a number, but instead the user enters a string, this causes data-type errors to occur in the program.

Another example of runtime errors is division by zero. This happens when the divisor is zero for integer divisions. For instance, the program in Listing 1.5 would cause a runtime error, as shown in Figure 1.11.

3. Logic Errors

Logic errors occur when a program does not perform the way it was intended to. Errors of this kind occur for many different reasons.

For example, suppose you wrote the program in Listing 1.6 to convert Celsius 35 degrees to a Fahrenheit degree:

You will get Fahrenheit 67 degrees, which is wrong. It should be 95.0. In Java, the division

for integers is the quotient—the fractional part is truncated—so in Java 9 / 5 is 1. To get the correct result, you need to use 9.0 / 5, which results in 1.8. In general, syntax errors are easy to find and easy to correct because the compiler gives indications as to where the errors came from and why they are wrong. Runtime errors are not difficult to find, either, since the reasons and locations for the errors are displayed on the console when the program aborts. Finding logic errors, on the other hand, can be very challenging. In the upcoming chapters, you will learn the techniques of tracing programs and finding logic errors.

1.10.4 Common Errors

Missing a closing brace, missing a semicolon, missing quotation marks for strings, and misspelling names are common errors for new programmers.

Common Error 1: Missing Braces

The braces are used to denote a block in the program. Each opening brace must be matched by a closing brace. A common error is missing the closing brace. To avoid this error, type a closing brace whenever an opening brace is typed, as shown in the following example.

Common Error 2: Missing Semicolons

Each statement ends with a statement terminator (;). Often, a new programmer forgets to place a statement terminator for the last statement in a block, as shown in the following example.

Common Error 3: Missing Quotation Marks

A string must be placed inside the quotation marks. Often, a new programmer forgets to place

a quotation mark at the end of a string, as shown in the following example.

If you use an IDE such as NetBeans and Eclipse, the IDE automatically inserts a closing

quotation mark for each opening quotation mark typed.

Common Error 4: Misspelling Names

Java is case sensitive. Misspelling names is a common error for new programmers.

For example, the word main is misspelled as Main and String is misspelled as string in the following

code.

CHECK-POINT

1.42 What are syntax errors (compile errors), runtime errors, and logic errors?

1.43 Give examples of syntax errors, runtime errors, and logic errors.

1.44 If you forget to put a closing quotation mark on a string, what kind error will be

raised?

1.45 If your program needs to read integers, but the user entered strings, an error would

occur when running this program. What kind of error is this?

1.46 Suppose you write a program for computing the perimeter of a rectangle and you

mistakenly write your program so that it computes the area of a rectangle. What kind

of error is this?

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Lesson 7: Creating, Compiling, and Executing the program

Note: Before you start to code you need to download the API or JDK (Java Development tool kit) that  you can download on the internet. You may click the link below.

Java Development tool kit download link👈👈👀

CREATING

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1. public class Welcome 

2. {

3.   public static void main(String[] args)

4.    {

5.   System.out.println("Welcome to Java!");

6.    }

7. }

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COMPILING

EXECUTING THE PROGRAM

1st. You need to go to the folder where you save your Java program code.

Executing using CMD prompt or command prompt

1st Step

Step 2

3rd Step

4th step

CHECK-POINT

1.28 What is a keyword? List some Java keywords.

1.29 Is Java case sensitive? What is the case for Java keywords?

1.30 What is a comment? Is the comment ignored by the compiler? How do you denote a

comment line and a comment paragraph?

1.31 What is the statement to display a string on the console?

1.32 Show the output of the following code:

Note:

1. Please write your answers on a piece/s of bond paper

2. Please observe a margin.

3. No erasures; and

3. Write legibly.

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Thank you God bless!

Lesson 6: Simple Program

 

A Java program is executed from the main method in the class.

Let’s begin with a simple Java program that is displays the message welcome to Java! On the console (output).

The word console is an old computer term that refers to the text entry and display device of a computer. 

Console input means to receive input from the keyboard, and console output means to display output on the monitor.

Line 1 - defines a class. Every Java program must have at least one class. Each class has a

name. By convention, class names start with an uppercase letter. In this example, the class

name is Welcome.

Line 2 - defines the main method. The program is executed from the main method. A class

may contain several methods. The main method is the entry point where the program begins execution.

A method is a construct that contains statements. The main method in this program contains the System.out.println statement. This statement displays the string Welcome to Java! On the console (Line 4).

String is a programming term meaning a sequence of characters. A string must be enclosed in double quotation marks. Every statement in Java ends with a semicolon (;), known a the statement terminator.

Reserved words, or keywords, have a specific meaning to the compiler and cannot be used for other purpose in the program.

For example, when a compiler sees the word class, it  understand that the word after class is the name for the class. Other reserved words in this program are public, static, and void.

Line 3 is a comment that documents what the program is and how it is constructed. Comment help programmers to communicate and understand the program. They are not programming language and thus are ignored by the compiler.

In Java, comments are preceded by two slashes ( //) on a line, called a line comment, or enclosed between / * and */ on one or several lines, called a block comment or paragraph comment. When compiler sees //, it ignores all text after // on the same line

The following below are the example of comments:

A pair of curly braces in a program form a block that groups the program’s components. In Java, each block begins with an opening braces ({) and ends with a closing braces (}).

Every classes has a class block that groups the data and methods of the class. Similarly, every method has a method block that groups the statement in the method.

Blocks can be nested, meaning that one block can be placed within another, as shown in the following code below.

`~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~'

You have seen several special characters

(e.g., { }, //, and ;) in the program. They are used in almost every program. The most common errors you will make as you learn to program will be syntax errors.

'~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.'

.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~

Check-Point

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   ~o~ End of the lesson ~o~

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Thank you!

Lesson 5: Java Specification

 Good day my dear students!!

    We are almost there... Next week we are going to do the actual coding, so I suggest to study in advance for you to go along with the application next week. You may download the previous lessons from lesson 1 to 6 by clicking the link below and please answer the check-point 4 and 5 for your assignment.

Note: No assignment, No entry in the computer lab.

Download: Lessons 1 to 6 (Click here)👈👈

*** LESSON FIVE (5) ***

**JAVA LANGUAGE SPECIFICATION **

👉 is a technical definition of the Java programming language’s Syntax and semantics.

**JAVA SYNTAX **

👉 is defined in the Java specification

**API**

👉also known as library, contains predefined classes and interfaces for developing Java programs.

**JDK**

👉Java Development Toolkit

Example of Java development toolkit are the following:

NetBeans, Eclipse, and Textpad

**IDE**

👉is defined in the Java API

(Integrated Development Environment)

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Note:

Computer languages have strict rules of usage. If you do not follow the rules when writing a programs, the computer will not be able to understand it.

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Java is a full-fledged and powerful language that can be used in many ways it come in three edition: 

Java Standard Edition (Java SE) to develop client-side applications. The applications

can run standalone or as applets running from a Web browser.

 Java Enterprise Edition (Java EE) to develop server-side applications, such as Java

servlets, JavaServer Pages (JSP), and JavaServer Faces (JSF).

 Java Micro Edition (Java ME) to develop applications for mobile devices, such as

cell phones.

Check-point

Instruction: Read the question carefully and write the correct answer after each and every question. You may use 1/2 sheet of paper this time. Please write your answer neatly and legibly.

1.24 What is Java Language specification?

1.25 What does JDK stand for?

1.26 What is IDE stand for?

1.27 What is Java Syntax?

1.28 Discuss the different version of Java.

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Thank you and God bless!

Lesson 4: Java, the World Wide Web, and beyond

 

Java has become enormously popular. It is rapid rise and wide acceptance can be traced to its designed characteristics, particularly its promise that you can write a program once and run it anywhere.

As stated by its designer Java is:

SIMPLE

OBJECT ORIENTED

DISTRIBUTED

INTERPRETED

ROBUST

SECURE

ARCHETECTURE NEUTRAL, 

PORTABLE

HIGH PERFORMANCE

MULTI-THREADED; AND DYNAMIC

Java is full-featured, general-purpose programming language that can be used to develop  robust mission-critical applications.

Today, it is employed not only for Web programming but also for developing standalone applications across platforms on servers, desktop computers, and mobile devices.

Instruction: Read the question properly and Write your answer on a 1/2 sheet of paper and submit it next meeting (August 22, 2023).

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Thank you and God bless you...

Lesson 3: Operating System

Greetings!

Good day everyone please have time to study because we are going to have a Weekly test on Tuesday (August 14, 2023) I already gave you a hard copy last meeting so that you could study from Lesson 1, 2 and 3 and you may download the ppt below for your convenient. Thank you and see you in my class.

Lesson 3: Operating System

What is an Operating System?
Is the important program that runs on a computer.
The OS manages and control a computer's activity.
Popular operating system for general-purpose computers;
* Windows
* Mac OS
* Linux
Function of OS
* Providing a user interface
* Running application
* Support for built in utility
* Control to the computer hardware
Components of OS
* Process Management
* Memory management
* I/O device management
* Network management
* User interface
Types of OS
* Single user, single task
This type of operating system only has to deal one person at a time,
running one user application at a time.
example: Nokia mobile phone (Symbian), Palm OS- hand held computers.
* Single user, multi-tasking
a. Windows - allows user to perform one or more than one task at a time
-Commonly as; MS windows and Apple Macintosh
-Windows is a series of operating systems developed by Microsoft
each version of windows includes graphical user interface, with desktop that allows users to view files and folder.
b. Android OS now a days is a Single user, multi-tasking because of its multi-tasking features.
c. Macintosh -OS X is version 10 of the Apple Macintosh operating system.
-OS X was described by apple as its first complete revision of the previous version OS 9, with a focus on modularity so that   future changes would be easier to incorporate.
  - Written in C++, C. Objective -C
Operating System interface
* Command line interface
* Graphic user interface
Advantages of OS
* Easy to use
* User friendly
* Intermediate between all hardware's and software of the system.
* No need to know any technical languages
* It’s the platform all programs.
Disadvantages
* If any problems affected in OS, you may lose all the contents which have been stored already
* Unwanted user can use your own system. (Wireless desktop) and computer hacking. 

Check-Point
1. What is an Operating System?
2. What are the 3 prominent operating systems for general-purpose computers?
3. What are the functions of an Operating system.
4. Name the 2 types of OS.
5. Name two (2) Operating system interface.
6. Name the advantage and disadvantages of an operating system.

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   ~o~ End of the lesson ~o~

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Thank you and God bless!

Lesson 2: PROGRAM

Please click and download the following links below for your reference and for your 1st performance task. (Please take note for the deadline of submission will be on Tuesday - August 8, 2023 and we're going to have a summative test on the same date.)

Performance task ( Project no. 1)

Click here to get the copy of the PPT file

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   ~o~ End of the lesson ~o~

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Thank you and God bless...