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abstract

speech and thoughts

Describe facts in more general, less concrete terms.

access modifier

instance methods

Private and public are access modifiers that control who is allowed to access a variable or call a method (visibility of a variable or method).

Lesson 157

access modifier

instance variables

accessor method

Getter- or setter-method that is intended to read or write a private attribute.

algorithm

A sequence of instructions that can solve a class of specific problems.

Lesson 39

API (application programming interface)

Public parts of a software component that are intended to be used by others. The class String with all its public methods is part of the Java-API. But the internal implementation of the class String is kept private and not part of the Java-API.

Lesson 189

Apple Silicon

Processor architecture of modern macOS computers.

argument

method call

A value passed to a method during a method call.

arithmetic operator

Operators that calculate something like plus, multiplication etc.

array

An ordered set of multiple variables of the same data type that can be accessed using an index. The size of the array is fixed and can not be changed once the array is created.

Lesson 200

array initializer

A comfortable way to initialize an array. An array initializer consists of comma separated elements that are surrounded by a pair of braces.

Lesson 215

ASCII (American Standard Code for Information Interchange)

character set

The standard was created in the sixties and contains 128 different characters, mainly the characters of an english keyboard.

assignment

Storing a value in a variable.

attribute

In the real world color is a property, an attribute of a vehicle. In our program color is an instance variable, an attribute of the class Vehicle.

auto-unboxing

Auto-unboxing is performed by the Java compiler in situations where an object is provided, but a primitive value is required. Please note that auto-unboxing causes a NullPointerException if the provided object is null.

autoboxing

Autoboxing takes place in situations where an object is required, but a primitive value is provided. Autoboxing is null-safe.

backslash

The character \ that is used to introduce escape sequences in a Java string.

bit

A bit is either 0 or 1, the smallest information unit in computer science.

block

Code beginning with an opening brace and ending with a closing brace is called a block.

Lesson 26

boolean expression

logical operators

An expression that is evaluated to a boolean value. A boolean expression is always evaluated to either true or false and is often used as condition in if-statements or loops.

Lesson 69

boxing

Creating a wrapper object from a primitive value is called boxing.

branch

Part of an if-statement that is executed if a certain condition is met. An if-statement always has an if branch and can have one or more else-if branches and finally can have an else branch.

Lesson 66

breakpoint

Tells the debugger where he should pause our program during debugging. Pausing a program is also called interrupt program execution.

bug

Used in the modern computer world as a synonym for a software error.

byte

A sequence of 8 bits.

byte code

In Java the source code is not directly translated into machine code. Instead, the translation from source code to machine code is performed in two independent steps. In the first step the source code is translated into an intermediate language called Java byte code. Java byte code is platform independent.

call a method

Tell Java to execute the code block of a certain method. The control flow jumps into the called method and will later return to the caller.

CamelCase

variable name

Writing the first letter of each word in upper case. Used to visually separate words in identifiers (spaces are not allowed in identifiers). For example: menuSelection, mySpecialMethod()

case label

Introduces each branch of a switch-statement.

case-insensitive

Compare of strings

The string compare does not distinguish between upper and lower case letters. "Hello" and "hello" are, f. e., considered to be the same string.

case-sensitive

identifier

Identifiers in Java are case-sensitive: The identifiers selection and Selection are considered two different identifiers, since upper and lower case letters make a difference.

case-sensitive

Compare of strings

The string compare distinguishes between upper and lower case letters. "Hello" and "hello" are, f. e., considered to be different strings.

central processing unit (CPU)

Main part of a computer and can essentially do three things: load data, manipulate data and store data.

char

Primitive data type for a single unicode character.

character

In programming the technical term character refers to a letter, a digit and so on, not to the characteristics of a person.

character encoding

All data a computer processes is internally represented as a sequence of zeros and ones. If you want to store characters in a computer you need a mapping between numbers and characters. The mapping between numbers and characters is called character encoding.

character set

A set of characters.

charset

see character set

class

In Java an object data type is called a class.

class file

The Java compiler creates a class file for each Java source file (class). The class file has exactly the same name as the source file but has the filename suffix class. Class files contain Java byte code in a binary format that is machine-readable, but not human-readable.

class variable

A class variable only exists once and is shared among all instances.

Lesson 229

comment out

A line that is contained in the source code but ignored by Java.

comparison operator

Operator that is used to compare two values.

compile

The source code is compiled (translated) into byte code. The compilation is performed by a tool called Java compiler.

compile time error

An error that occurs during compiling the source code is called compile time error. If we, for example, have a typo in a variable or method name the compiler raises an error. Compile time errors are displayed in the IDE during the development of our program. Fixing a compile time error is much easier and cheaper than fixing a runtime error.

compiler

The tool that compiles (translates) the source code into byte code is called compiler. The compiler is the most important tool of the JDK.

compound expression

An expression that is composed of multiple expressions.

concat operator

Operator that concatenates two string operands. See string concatenation.

concatenate

see string concatenation

concatenation

see string concatenation

condition

A boolean expression that is always evaluated to either true or false.

console

The console is a simple window without any graphical elements that only can display text to the user and read text input from the user.

console application

A console application has no graphical elements and is restricted to text output and text input. Each console application has an associated console window.

constant

A variable that contains a primitive value or a constant reference. The value of the variable can not be changed. Please note that in case of a reference only the reference itself is constant, the referenced object can still be changed.

Lesson 235

constructor

A constructor is a special kind of method that can be used to initialize a newly created instance. The name of the constructor has to match exactly the name of the containing class including lower and upper case letters.

control flow

definition

The chronological sequence in which the statements of a program are executed is called control flow or program flow.

control flow

if

control flow

nested loops

Lesson 81

control flow statement

if

A statement that controls the program flow, f. e. an if-statement or a switch-statement.

control flow statement

loops

control structure

if

A programming construct that affects the control flow, f. e. an if-statement or a loop.

control structure

loops

data type

Kind of data stored in a variable. In Java there are data types for integer numbers, text etc.

debug mode

debugging a program

Execute our program step by step. We can pause execution before every statement to inspect the value of variables and watch, what our program is doing in detail.

debugger

vislualize control flow

Very powerful tool, that assists us in finding bugs.

debugging

vislualize control flow

The procedure of searching for bugs in the software.

declare a method

Tell Java that there is a method with a certain name, arguments and return type. Provide a code block that should be executed if the method is called. Please note that the statements not get executed until the method is called.

default constructor

A constructor that does not have parameters is called default constructor.

default label

The default branch of a switch-statement is executed if none of the case branches was executed. Similar to an else branch of an if-statement.

default package

A package that contains classes that are not explicitly declared in a package. These classes are directly placed in the source folder and do not have a package statement. It's not recommended to use the default package, because sooner or later it may cause problems.

Lesson 184

default values

instance variables

After an instance is created all instance variables are automatically initialized with technical default values. In a constructor some instance variables may be manually initialized with more useful values.

do-while loop

A foot-controlled loop that is often used for loops that should be executed at least once.

dynamic data

Data that is intended to be changed during program execution. In a real world application, dynamic data would be loaded from a database for example.

Lesson 86

element

The values or references stored in an array are called elements.

Lesson 200

empty string

A string that does not contain any characters. An empty string has the length 0. Please distinguish between an empty string and the special value null.

Lesson 121

encapsulate

Implement a certain logic in a single code location or at least in a single class.

Lesson 139

encapsulate

private instance variables

Protect internal state against uncontrolled access from outside the class. Make attributes private and only offer appropriate access methods.

Lesson 175

encapsulation

see encapsulate

Lesson 139

endless loop

see infinite loop

entry point

program execution

The point where the execution of our program starts. In every Java program, the main-method is the entry point.

escape sequence

String

The backslash together with the following character is called an escape sequence and can be used to insert some special characters into a string literal.

escape sequence

char

escaping a character

The backslash is a meta character that gives the following character a special meaning that differs from the standard meaning of that character. Giving the following character a special meaning is called escaping a character.

evaluate

condition

Reduce an expression to a value.

evaluate an expression

Reduce an expression to a single value.

evaluating

condition

see evaluate

evaluation

condition

see evaluate

evaluation of an expression

see evaluate an expression

exception

see runtime error

explicit declaration

default constructor

When we do not explicitly declare a constructor in a class, Java implicitly declares a default constructor for us to ensure that the class can be instantiated.

explicit return type

constructor

A constructor has no explicit return type but the implicit return type is always the class in which the constructor is declared.

expression

Consists of variables, operators and method calls and is evaluated to a single value.

fall through

see fall-through

fall-through

If a break statement is missing at the end of a case block the control flow falls through and program execution is continued with the statements below the next case label.

flag

A synonym for a boolean value. A vehicle, f. e., can be flagged as sold or not.

Lesson 79

floating point division

A division with at least one floating point number as operand. Decimal places are retained.

floating point number

Can store decimal places.

foot-controlled loop

A loop like the do-while loop where the termination condition is checked each time after the loop body has been executed. The loop body of a foot-controlled loop is executed at least once.

for loop

A head-controlled loop that is often used to iterate through an array if an iteration counter is needed.

Lesson 207

for-each loop

A head-controlled loop that is often used to iterate through an array if no iteration counter is needed.

Lesson 210

formatting of source code

line break

Insert additional whitespaces (spaces, tabs and line breaks) into the source code to increase the readability of the source code for humans.

fully qualified class name

The package name followed by a dot as separator and the class name is called a fully qualified class name (FQCN). A FQCN is unique in the whole application. java.lang.String is an example for a fully qualified class name.

Lesson 185

functional

In programming we often distinguish between the functional point of view and the technical point of view. The functional point of view is related to our business requirements and is interested in what the application does. The technical point of view is related to the implementation and is interested in technical details.

functional requirements

Requirements that are related to the functionality of our software. With the implementation of these requirements we changed the functionality of our software.

generic code

Source code that is more generally usable, because it's less specific is called generic code.

Lesson 201

getter

Method that is intended to read a private attribute.

GUI (graphical user interface)

Graphical elements a user can use to interact with a computer program.

GUI application

An applications where the interface between the user and the computer consists of graphical elements.

hard disk (HDD)

Long-term storage, sometimes called permanent storage, that can store data without being connected to the power supply. Mostly cheaper than a SSD.

head-controlled loop

A loop like the while loop where the termination condition is checked each time before the loop body is executed. The loop body of a head-controlled loop may never be executed.

high-level programming language

In a high-level programming language we can write our source code in a human-readable way and use programming constructs such as classes, loops, statements and so on.

IDE (Integrated development environment)

An IDE is a very powerful computer program that assists us in writing own computer programs. The IDE is the most important tool for a software developer.

Lesson 4

identifier

definition

Unique name for a variable, constant, method or class.

identifier

variable name

identifier

method name

Lesson 96

identifier

class name

Lesson 146

identifier

constant name

Lesson 236

immutable object

An object that can not be modified is called immutable object. A good example of an immutable object is a String. An immutable object is a design decision, not a special technical feature.

Lesson 235

implement

Writing program code, that solves a certain problem.

implement an algorithm

Write a computer program, that follows the instructions of an algorithm.

Lesson 39

implementation

The program code, that solves a certain problem is often called implementation.

implicit declaration

default constructor

When we do not explicitly declare a constructor in a class, Java implicitly declares a default constructor for us to ensure that the class can be instantiated.

implicit return type

constructor

A constructor has no explicit return type but the implicit return type is always the class in which the constructor is declared.

import statement

Importing the class Scanner means to let Java know that we would like to use the class java.util.Scanner under the simple name Scanner.

Lesson 185

increment

loop variable

Adding the value one to a variable is called to increment a variable.

Lesson 82

increment

a variable

Lesson 202

index

The storage spaces for the elements of an array are ordered. The number of the storage space is called index. The first element is stored at index 0, the last element is stored at the index array.length - 1.

Lesson 200

index variable

array

A variable that contains the index of an array. By incrementing an index variable in a loop, we can iterate through an array.

Lesson 201

infinite loop

A loop that runs for ever. The termination condition is always true.

initialization

Assign an initial value to the variable. In our example with the sorting box, initializing a variable means: putting something into the drawer for the first time.

inner loop

A loop that is contained in the loop body of another loop.

Lesson 78

instance method

An instance method has access to the instance variables of the class in which the method is declared.

Lesson 157

instance variable

simplified

An instance variable exists once for each instance of the class in which it is declared.

Lesson 86

instance variable

access from other class

Mostly used as synonym for an attribute.

instruction set

The set of different instructions a CPU can execute is called instruction set.

integer division

A division with two integer numbers as operands. The decimal places are truncated. Please note that the result is not rounded.

internal state

of an instance / object

The attributes of an object represent the internal state of that object.

Lesson 175

interpret

The JVM interprets Java byte code and generates machine code during execution of a Java program.

interpreter

A tool that interprets Java byte code is called interpreter.

interrupt program execution

debugging a program

Pausing program execution at a breakpoint for debugging purposes.

invoke a method

see call a method

iterate

Walk through an array and visit every element once. Usually visiting means doing the same with each element, f. e., printing it to the console.

Lesson 202

iteration

The process of iterating an array is called iteration. Also see iterate.

Lesson 202

jar file

A jar file contains all our classes with the byte code, some extra files called resources like pictures, sounds and so on and some metadata, for example, to tell Java which class contains the main method. Technically, a jar file is a zip archive just with a different file suffix.

Java

Java is an awesome programming language and is perfectly suited for learning the basics of programming. In the business world, Java is one of the most frequently used programming languages.

Lesson 2

JavaDoc

The awesome documentation standard for Java-APIs.

Lesson 189

JDK (Java Development Kit)

The JDK contains several tools that are required to develop Java software. The compiler is the most important tool of the JDK.

JRE (Java Runtime Environment)

The environment in which our Java programs are executed. A JDK also contains a JRE.

JVM (Java Virtual Machine)

The JVM is a computer program that translates every byte code instruction during program execution into native machine code of the CPU. We say that the JVM interprets Java byte code. The JVM is part of the JRE.

key word

see keyword

keyboard focus

A window that can receive keyboard input has the keyboard focus. Only one window can have the keyboard focus at a time, and all keyboard input is send to this window.

keyword

Reserved word that has a special meaning in Java (f. e. int). It's not allowed to use a keyword as name for a variable, constant, method or class.

left operand

In the expression 5 + 7, the left operand is 5.

line comment

A single line that is commented out.

literal

A value that is directly written in the source code.

literal

boolean

A boolean value that is directly written in the source code. Either true or false.

Lesson 79

loop

Programming construct that can execute a code block multiple times depending on the termination condition.

loop block

see loop body

loop body

Part of the loop that is repeatedly executed (between the opening brace and the closing brace of the loop). Also called loop block.

loop counter

while loop

A variable that counts the number of loop passes.

Lesson 82

loop pass

One execution of the loop block. Usually, we have several loop passes, before the loop is terminated.

machine code

The instructions that consist of a sequence of zeros and ones are called machine code.

main memory (RAM)

see RAM

meta character

A character that has a special meaning.

method

A group of statements that can be executed and has a unique name. A method can receive arguments and return a value.

modifier

The keywords public, private, static and final are called modifiers. To increase the readability of the source code for humans we should by convention write the modifiers in the recommended order (public/private, static, final).

Lesson 235

module

In real projects modules are used, f. e., to split up big programs in independent parts or to reuse software components. Please note that the way I use modules here is for didactic reasons only. Please never use modules in real projects for keeping up different versions of your source code. There are so-called version control systems that are used for that purpose.

Lesson 184

modulo

Rest of an integer division. 13 modulo 5 is 3.

Lesson 40

native machine code

Specific machine code for a certain processor architecture. A CPU can only execute native machine code.

nested inner block

A block that is placed inside another block.

nested loops

A loop that is contained in the loop body of another loop.

Lesson 78

non-functional requirements

Requirements that do not change the functionality of our software. Non-functional requirements can be related to security or maintainability for example.

null-safe

An implementation is called null-safe if it works properly although a reference is null.

Lesson 124

NullPointerException

If we try to access a variable or call a method using a null reference, we receive a NullPointerException.

Lesson 122

object data type

definition

Ab object data type can be composed of several values, f. e., String that is composed of several characters. Java is shipped with several object data types (classes) such as String or Scanner. We can define own object data types. Object data types can be null and can have methods.

Lesson 125

object data type

own object data types (classes)

oop (object-oriented programming)

Models parts of the reality by using classes, objects and encapsulation as central programming technique.

operator

assignment

= is an operator, for example.

operator

In the expression 5 + 7, the operator is +.

operator precedence

Determines the sequence, in which Java executes operators. Operators with a higher precedence are executed before operators with a lower precedence. The multiplication operator, f. e., has a higher precedence than the addition operator. Therefore, the multiplication operator is executed before the addition operator.

outer loop

A loop that contains in its loop body another loop.

Lesson 78

own data type

In Java we can define own data types with certain attributes and methods.

parameter

method declaration

A value received in a method implementation during a method call.

platform

The combination of a processor architecture and an operating system is called platform. Common platforms are Windows on x64 or macOS on Apple Silicon.

platform-independence

Java byte code is platform-independent, because it can be executed on any platform for that an appropriate JRE exists.

point before dash calculation

One concrete example for operator precedence.

precedence of operators

see operator precedence

primitive data type

A primitive data type contains a single value, f. e., an integer number (primitive data type int). Java has 8 builtin primitive data types. We can not define own primitive data types. Primitive data types can not be null and can not have methods.

Lesson 125

private

instance variables

Access modifier. Private attributes and methods are only accessible within the class that declares the attribute or method.

processor architecture

"Type" of processor. In the market there are different processor architectures each with its own instruction set.

program

A set of instructions that are executed by our computer.

program flow

property

Mostly used as synonym for an attribute.

pseudocode

A mixture of natural language and programming constructs that is written directly into the source in the form of comments and is completely free of any form. Maybe helpful in understanding and solving problems.

Lesson 51

public

instance variables

Access modifier. Public attributes and methods are also accessible from outside the class that declares the attribute or method.

RAM (random access memory)

Used to store data. The main memory can store data as long as the computer is switched on.

refactoring

definition

Reorganizing source code to increase maintainability. During a refactoring parts of our source code are reorganized without changing functionality.

refactoring

rename variable

Lesson 102

relational operator

see comparison operator

return statement

method

Immediately terminates a method call and might return a value to the caller. Control flow jumps back to the caller. In concrete to the first statement behind the method call.

return type

method

The data type that is returned from a method to the caller of the method.

return value

method

A value returned from a method to the caller of the method.

right operand

In the expression 5 + 7, the right operand is 7.

run mode

starting a program

The program is started and executed as fast as possible. The program is only paused sometimes to wait for user input.

runtime error

An error that occurs during running the program is called runtime error or exception. If we, for example, try to call an instance method on a reference that is null, the JVM throws a NullPointerException. Runtime errors occur at the customer while the program is running or at the developer while the program is tested. Fixing a runtime error is more expensive than fixing a compile time error.

scope

loops

Lesson 81

scope

instance variables

scope (range of validity)

local variable

The range, within a variable can be accessed.

self defined data type

see own data type

setter

Method that is intended to write a private attribute.

shadowing

visibility of a variable

A variable that is still valid but not visible, because there is another variable with the same name in an inner scope. A local parameter, f. e., shadows an instance variable with the same name.

Lesson 167

signed data type

A data type that can store negative and positive values. Java only offers signed data types.

simple class name

A class name without the package name is sometimes called simple class name.

Lesson 185

solid state disk (SSD)

Long-term storage, sometimes called permanent storage, that can store data without being connected to the power supply. Mostly faster than a HDD.

source code

The origin, the source of our running program is our source code, that's why it's called source code.

sources

Short for source code.

statement

A statement is like a command that is executed by Java.

static variable

see class variable

Lesson 229

String

Object data type shipped with Java that stores text (a sequence of characters).

Lesson 60

string concatenation

Create a new string that contains the characters of two other strings. First all characters of the left string then all characters of the right string.

String literal

A String that is directly placed in the source code, f. e. "Hello".

Lesson 60

structured data

Store data in dedicated attributes with appropriate data types. Like a spread sheet that has separate columns for each attribute.

Lesson 134

switch expression

The expression used in a switch statement. Can be a String or an integer number, for example.

switch statement

Control structure that can sometimes be used to replace an if-statement with several branches.

symbol

identifier

The word symbol is often used in error messages as synonym for identifier (name of a variable, constant, method or class).

syntax

Rules how to form a correct statement or a correct program.

Lesson 20

syntax error

If a syntax rule of a programming language is violated we call this a syntax error.

Lesson 20

technical

In programming we often distinguish between the functional point of view and the technical point of view. The functional point of view is related to our business requirements and is interested in what the application does. The technical point of view is related to the implementation and is interested in technical details.

termination condition

A condition that controls if a loop is continued (the loop block is executed once again) or terminated. If the termination condition is evaluated to true the loop is continued. If the termination condition is evaluated to false the loop is terminated. The technical term 'termination condition' is misleading. Maybe the term 'continuation condition' would be more precise.

to refactor

see refactoring

truth value (boolean)

A value that is either true or false.

Lesson 79

type cast

A type cast is an conversion of a value into another data type. There are explicit type casts that are explicitly written in the source code and implicit type casts that are automatically performed by Java. Please note that the type cast operator only converts a temporary value that is produced by the right operand. The original variable is never changed.

Lesson 223

type conversion

Converting the type of a value to another type. For example the int 0 to the double 0.0

type safety

Java always wants to know, which kind of data is stored in a variable and prevents us from storing data with an incompatible data type in our variable.

type-safe

see type safety

unboxing

Reading out a primitive value from a wrapper object is called unboxing.

unicode

character set

Java uses the so-called unicode character set that contains about 150 thousand different characters. The first 128 characters are the same as in ASCII, so that unicode is downward compatible to ASCII.

unsigned data type

A data type that can store only positive values including zero. Java does not offer any unsigned data types.

unstructured data

Store data, f. e. in a long string that contains values for several attributes that should be separated from a functional point of view.

Lesson 134

variable

We store data in variables. A variable is like a drawer of a sorting box.

version control system

Essential tool used in almost every software project to track changes to the source code.

Lesson 184

visibility

local variable

see visible

visibility

private instance variables

visible

local variable

A variable is visible if it can be seen from the current position.

while loop

A head-controlled loop that is often used for loops that might never be executed.

whitespace

"Invisible" character. For example: spaces, tabs and line breaks.

Lesson 20

wrap a line

formatting

Break up a long line into multiple lines to increase the readability of the source code for humans. Part of formatting.

wrapper class

Wraps a primitive value in an object data type and offers methods to convert between a primitive value and an instance of the wrapper class. Java provides a wrapper class for each primitive data type.

wrapper type

see wrapper class

x64 architecture

One of the most popular processor architectures is the x64 architecture and is used by most Windows and Linux computers.