Learn java in one day pdf download

These topics include object- oriented programming concepts, error handling techniques, file handling techniques and more. In addition, new features of Java such as lambda expressions are also covered. All examples in the book are carefully chosen to demonstrate each concept so that you can gain a deeper understand of the language. In addition, as Richard Branson puts it: "The best way of learning about anything is by doing".

The project uses concepts covered in the book and gives you a chance to see how it all ties together. For feedback or queries, you can contact me at jamie learncodingfast. Chapter 2: Getting Ready for Java 2. Reference Type 4. Whether you are a seasoned programmer or a complete novice, this book is written to help you learn Java programming fast. Topics are carefully selected to give you a broad exposure to the fundamental concepts of Java while not overwhelming you with information overload.

While it is not possible to cover every single Java concept in this book, rest assured that by the end of the book, you should have no problem writing your own Java programs. In fact, we will be coding a program together as part of the project at the end of the book.

Ready to start? Java is an object-oriented programming language developed by James Gosling at Sun Microsystems, which has since been acquired by Oracle Corporation. It was released in and is currently one of the most popular programming languages in use. It can be used to develop applications for a large variety of environments, such as applications for desktop, web and even mobile devices. One of the main features of Java is that it is platform independent.

This means that a program written in Java can be executed on any operating system such as Windows, Mac or Linux. Like all modern programming languages, Java code resembles the English language which computers are unable to understand. Therefore, Java code has to be converted into machine code through a process known as compilation.

Every computer platform has its own machine code instruction set. Hence, machine code that is compiled for one platform will not work on another platform. Java does it a little differently. Instead of compiling into machine code directly, Java compiles all written code into bytecode first. Bytecode is platform independent. That is, there is no difference between the bytecode for Windows, Mac or Linux.

The advantage of using this two-step compilation process is that it allows Java code to be run on all platforms as long as the computer running the Java program has JVM installed. JVM is free to download and there are different versions for different computer platforms. There are a lot of reasons why one should learn Java. Firstly, Java is currently one of the most popular programming languages in use.

According to Oracle, 3 billion devices run Java. Furthermore, Android apps are also developed using Java. With the growing demand for mobile apps, it is safe to say that Java is an essential language to learn if you are interested in becoming a programmer.

If you have any prior programming experience, you will find learning Java a breeze. Even if you are totally new to programming, you can rest assured that Java is designed to be a relatively easy language to learn. Java is also designed to be platform independent.

As mentioned earlier, Java code is compiled into bytecode first, which can be run on any machine that has the Java Virtual Machine. Hence with Java, you can write the code once and run it anywhere you want.

Next, Java is an object-oriented programming OOP language. Object- oriented programming is an approach to programming that breaks a programming problem into objects that interact with each other.

Once you master Java, you will be familiar with these concepts. This will make it easier for you to master other object-oriented programming languages in future. Convinced that Java is a great language to learn? JDK stands for Java Development Kit and is a free kit provided by Oracle that contains a number of tools to help us develop Java applications. Some of these tools include a compiler to compile our written code into bytecode javac. If you are only interested in running Java programs, all you need is the JRE.

However, since we are also interested in developing Java programs, we need the JDK. Strictly speaking, we can develop Java applications without using NetBeans. We can write our code in Notepad or any other text editor and compile and execute them using the tools provided in JDK. The screenshot below shows an example of how this can be done. However, while it is possible to develop Java applications using the JDK alone, this process is tedious and error-prone.

To make coding easier, you are strongly encouraged to use an IDE. An IDE includes a text editor with advanced features for us to write our code, and provides us with a graphical user interface to debug, compile and run our applications. Go ahead and download the application.

Once you are done installing it, you are ready to start coding your first Java program. However, before we do that, I would like to highlight the fact that most of the code in Java consists of rather long statements. Hence, some statements may wrap around to the next line in this book. Click Next to continue.

On the next screen, name the project HelloWorld and take note of where the project is stored. Finally, click Finish to create the project. You will be presented with a default template that NetBeans created for you automatically. Replace the code in the template with the code below. Note that line numbers are added for reference and are not part of the actual code. You may want to bookmark this page for easy reference later when we discuss the program.

As you type, you will notice some interesting features of NetBeans. Different words serve different purposes in our program and are thus displayed using different colours. In addition, you will also notice that a box appears near the cursor with some help messages occasionally.

That is known as Intellisense. For instance, when you type a period. Finally, also note that NetBeans will automatically close brackets for you when you type an opening bracket. These are some of the features that NetBeans provides to make coding easier for us. You can then execute the compiled program by clicking on the Run button at the top menu refer to image below. If your program fails to run, there will be a pop up box with an error message.

Click Run Anyway to continue. You will then see a description of the error in the output window refer to next image. Alternatively, you can also hover your mouse over the red squiggly line in the text editor window. That will provide you with another clue about what went wrong.

Try to identify and correct the mistake and run the program again. If all goes well, you will see the following in the output window.

The other two sentences are additional information provided by NetBeans and are not part of our program output. You have successfully coded your first program. Give yourself a pat on the shoulders. The name of the Java file that you just wrote is HelloWorld. You can find the name at the top of the text editor window refer to image above.

A package is simply a grouping of related classes and interfaces. When we write package helloworld; at the top of our file, we are asking the compiler to include this file in the helloworld package. Files that belong to the same package are stored in the same folder. This folder stores the files of the helloworld package. It is a convention for us to name our packages in lowercase. Note that Java is a case-sensitive language. The advantage of declaring packages is that it prevents naming conflicts.

This is similar to how you can have two or more files of the same name on your computer as long as you put them in different folders. In addition to packages created by us, Java also comes with a large number of pre-created packages that contain code that we can use in our programs. For instance, code for input and output is bundled in the java.

To use these pre- written packages, we need to import them into our programs. For now, just know that in our example, the HelloWorld class starts on line 3 with an opening curly brace and ends on line 10 with a closing curly brace.

Curly braces are used extensively in Java to indicate the start and end of a code element. All opening braces in Java must be closed with a corresponding closing brace. Within the HelloWorld class, we have the main method which starts on line 5 and ends on line 8.

Whenever a Java application is started, the main method is the first method to be called. Notice the words String[] args inside the parenthesis of our main method? This means the main method can take in an array of strings as input. Do not worry about this for the moment. In our example, the main method contains two lines of code.

The second line System. Note that this statement ends with a semi-colon. All statements in Java must end with a semi-colon ;. After the System. You should now have a basic understanding of Java programming and be reasonably comfortable with NetBeans. A comment is actually not part of the program. It is added to our code to make it more readable for other programmers. As such, comments are not compiled into bytecode.

Variables are names given to data that we need to store and manipulate in our programs. For instance, suppose your program needs to store the age of a user. To do that, we can name this data userAge and declare the variable userAge using the following statement: int userAge; This declaration statement first states the data type of the variable, followed by its name.

In our example, the data type is int, which refers to integers. The name of our variable is userAge. After you declare the variable userAge, your program will allocate a certain area of your computer's memory space to store this data. You can then access and modify this data by referring to it by its name, userAge. These are known as primitive data types. The first 4 data types are for storing integers i. It uses 1 byte of storage space this is known as the width or the size of the data type.

We normally use the byte data type if storage space is a concern or if we are certain the value of the variable will not exceed the to range. It is the most commonly used data type for storing integers as it has the most practical range.

It is rarely used unless you really need to store a very large integer such as the number of inhabitants on Earth. In addition to having data types for storing integers, we also have data types for storing floating point numbers i.

It has a precision of about 7 digits. This means that if you use float to store a number like 1. By default, whenever you specify a floating point number in Java, it is automatically considered to be a double, not a float. Unless memory space is a concern, you should always use a double instead of a float as it is more precise. Besides the six data types mentioned above, Java has two more primitive data types. It uses 2 bytes of memory.

It is commonly used in control flow statements. However, the first character cannot be a number. Additionally, the dollar sign character is almost never used when naming a variable although it is not technically wrong to use it. Variable names should be short but meaningful, designed to indicate to the casual reader the intent of its use.

It makes more sense to name your variables userName, userAge and userNumber, instead of n, a and un. In addition, there are some reserved words that you cannot use as a variable name because they already have pre-assigned meanings in Java.

These reserved words include words like System, if, while etc. It is common practice to use camel casing when naming variables in Java. Camel casing is the practice of writing compound words with mixed casing, capitalising the first letter of each word except the first word e. Finally, variable names are case sensitive. This is known as initializing the variable.

You can change the value of the variable in your program later. There are two ways to initialize a variable. You can initialize it at the point of declaration or initialize it in a separate statement. The code below shows how you can initialize variables at the point of declaration line numbers on the left are added for reference and are not part of the code.

If we do not do that, the compiler will complain that the number is too large and give us an error. This is because by default, any floating point number is treated as a double by Java. Finally, when initializing a char data type, we need to enclose the character in single quotes as shown on line 9.

On line 12, we see an example of how you can declare and initialize two variables of the same data type in one statement. The two variables are separated by a comma, and there is no need to state the data type of the second variable. An example will likely clear this up. However, in programming, this is fine.

This statement means we are assigning the value of y to x. It is alright to assign the value of a variable to another variable. In our example, the value of x is now changed to 10 while the value of y remains unchanged.

Hence, y becomes 3 while the value of x remains unchanged i. However, if either x or y is a non integer, we will get a non integer answer. The decimal portion of the answer, if any, is truncated. Hence, we get 3 instead of 3. In all other cases, the result is a non integer as at least one of the operands is a non integer.

Note that 7. The former is a floating point number while the latter is an integer. Suppose we have the variable x, with an initial value of So eventually x becomes The same works for all the 5 operators mentioned in the section above.

This affects the order in which tasks are performed. Suppose we have an integer named counter. If we write System. In other words, it executes the tasks in this order System. This operator decreases the value of the variable by 1. This is known as type casting. If we want to convert a smaller data type into a larger data type, we do not need to do anything explicitly. For instance, the code below assigns a short 2 bytes to a double 8 bytes.

This is known as a widening primitive conversion and does not require any special code on our part. This is known as a narrowing primitive conversion. The example below shows how it can be done. Narrowing conversion is not safe and should be avoided unless absolutely necessary. This is because narrowing conversion can result in a loss of data.

When we cast The decimal portion is truncated after the conversion. We can also cast a double into a float. Recall that we mentioned earlier that all non integers are treated as double by default in Java?

If we want to assign a number like In addition to casting between numeric types, we can also do other types of casting.

Chapter 4: Arrays and Strings In the previous chapter, we covered the eight primitive data types in Java. Besides these primitive types, Java also comes with a few advanced data types. In this chapter, we are going to cover two of them: strings and arrays. In addition, we are going to discuss the difference between a primitive data type and a reference data type.

Note that you need to enclose the string in double quotes ". Specifically, it is an object of the String class. For now, all that you have to know is that the String class provides us with a number of pre-written methods that we can use when working with strings. A method is a block of reusable code that performs a certain task. In Java, a method may have different variations. Most of the examples below discuss only one of the variations for each method.

However, if you learn how to use one variation, you can figure out how to use the other variations with relative ease. We type the name of the method length in this case after the dot operator, followed by a pair of parenthesis. Most methods return an answer after they complete their tasks. The length method returns the length of the string.

You can assign this result to a variable as shown below. When you add the space between the two words, you get a total length of You can display the result of the length method using the statements below. Run the program. The toLowerCase method is used to convert a string to lowercase characters. We then assign the result to the variable uCase. Some methods in Java require certain data for them to work. These data are known as arguments. We include these arguments in the pair of parenthesis that follows the method name.

The substring method is an example of a method that requires one argument to work. The number 6 in the parenthesis is known as the argument. This argument tells the compiler where to start extracting the substring. Essentially, it is asking the compiler to extract the substring starting from index 6 i.

Note that in programming, index starts with a value of ZERO not 1. This is a common practice in almost all programming languages such as Python and Java. This result is then assigned to firstSubstring.

The substring method also comes with another variation that allows us to extract a substring from one index to another. We then use message to call the substring method. The two arguments are 1 and 8.

As before, the first argument tells the compiler the index of the starting position to extract. The second argument tells the compiler the index of the first position to stop extracting. In other words, in our example, the compiler stops extracting at position 8 not after position 8.

That means the letter at position 8 is not included in the substring. This character can then be assigned to a char variable. It returns true if the strings are equal and false if they are not. After splitting the string, the split method returns an array that contains the resulting substrings. An array is a collection of related data. We then use names to call the split method. The split method takes in one argument — the delimiter used to separate the substring.

In our example, the delimiter is a comma followed by a space. An array is a collection of data that are normally related to each other. Suppose we want to store the ages of 5 users. Instead of storing them as user1Age, user2Age, user3Age, user4Age and user5Age, we can store them as an array.

There are two ways to declare an array variable. The first way is to declare it as follows: int[] userAge; int indicates that this variable stores int values. However, this is not the preferred syntax in Java. After you declare an array variable, you need to create an array and assign it to the variable. Since userAge has not been assigned any array previously, this statement initializes userAge with the created array.

Once you initialize an array, the size of the array cannot be changed anymore. In this case, the array userAge can only hold 5 values from now onwards as we initialized it with 5 integers.

As we did not specify the values of these 5 integers, Java automatically creates an array using the default value and assigns it to userAge3. The default value for integers is 0.

You can update the individual elements in the array by accessing them using their indexes. Recall that indexes always start with a value of zero. The first element of the array has an index of 0, the next has an index of 1 and so forth. That is, 20 is added to the third element.

The methods that we discuss below are found in the java. Arrays class. To use them, you have to add the statement import java. This is to tell the compiler where to find the code for these methods. The import statement must appear after the package statement and before the class declaration. An example is shown below: package helloworld; import java. This is because the String class is present in the java. Now, let us look at some of the commonly used methods for arrays. It returns true if the arrays are equal and false if they are not.

Two arrays are considered equal if they have the same number of elements and the elements are arranged in the same order. This is because for result2, even though arr1 and arr3 have the same elements, the elements are not arranged in the same order. Hence, the two arrays are not considered equal. Note that in the example above, we added the word Arrays in front of the method name. This is because all methods in the Arrays class are static.

To call a static method, you have to add the name of the class in front. It requires three arguments. The second and third arguments tell the compiler at which index to start and stop copying respectively. In other words, in our example, we are copying elements from index 3 to index 6 i.

After copying the elements, the copyOfRange method returns an array with the numbers copied. This array is then assigned to dest. This makes it easy for us to display the contents of the array. It takes in an array as the argument. The sort method does not return a new array. It simply modifies the array that is passed in.

In other words, it modifies the numbers2 array in our example. You can then use the statement System. You will get [-2, 1, 5, 12, 14, 16] as the output.

To use this method, make sure your array is sorted first. You can use the sort method mentioned above to do so. This indicates that the number 78 is found at index 5.

There are two parts to this result — the negative sign and the number 4. The negative sign simply indicates that 39 is not found. The number 4, on the other hand, is kind of weird. It tells you where the number should be if it exists in the array.

The length of an array tells us the number of items the array has. Previously when we discussed strings, we mentioned we can use the length method to find the length of a string. Contrary to what most would believe, there is no length method when working with arrays.

Instead, to find the length of an array, we use the length field. For now, all you have to know is that to find the length of an array, you do not need to add parenthesis after the word length. Reference Type Now that we are familiar with strings and arrays, let us discuss an important concept regarding data types in Java.

All data types in Java can be classified as either a primitive type or a reference type. There are only 8 primitive types in Java byte, short, int, long, float, double, char and boolean , the rest are reference types. One of the main differences between a primitive type and a reference type is the data that is stored. A primitive type stores its own data. A reference type, on the other hand, does not store the actual data.

Instead, it stores a reference to the data. It does not tell the compiler what the value of the data is; it tells the compiler where to find the actual data. An example of a reference type is a String. The variable message stores the address of that memory location. As this is a book for beginners, we will not go into details about why reference types are necessary. Just be aware that there is a difference between primitive types and reference types; the former stores a value while the latter stores an address.

Immutable means the value of a string cannot be changed. Whenever we update a String variable, we are actually creating a new string and assigning the memory address to the String variable. The variable message stores the address of that location.

This new address is then assigned to message. This process is known as garbage collection and is handled automatically by Java. Chapter 5: Making our Program Interactive Now that we have covered the basics of variables and data types, let us write a program that accepts input from users, stores the data in a variable and displays messages to our users. After all, what good is a computer program if it cannot interact with its users?

Simply stated, to display outputs to our users, we can use the print or println method provided by Java. In order to use these methods, we have to add System. This is because the two methods belong to the PrintStream class and we have to use System. Do not worry if this sounds very confusing at the moment. The difference between the println and print methods is that println moves the cursor down to the next line after displaying the message while print does not.

For instance, if we write System. Other than that, the two methods are the same. Let us look at a few examples of how we can use println to display messages to our users. The print method works exactly the same way. Displaying a simple text message To display a simple message, we write System. Displaying the value of a variable To display the value of a variable, we pass in the variable name as an argument. Displaying results without assigning them to variables We can also use the println method to display the result of a mathematical expression or a method directly.

To display the result of a method, we can write System. I love Java. Finally, we can concatenate strings with mathematical expressions as shown below. This is to force the compiler to evaluate the expression first before concatenating the result with the other two substrings. You are strongly advised to do so whenever you concatenate strings with mathematical expressions. Failure to do so can result in errors. With it, a tab is printed. If you type System. However, sometimes we want to have greater control over the format of the output.

In that case, we can use the printf method instead to display the output to our users. The printf method is slightly more complex than the println method, but it offers more control over how our output is displayed. To format the output above, we can write System. The printf method requires one or more arguments. In the example above, we passed in four arguments to the method. These are known as format specifiers. They serve as placeholders and are replaced by the arguments that follow.

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