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Java is a programming language created by James Gosling from Sun Microsystems in 1991. The first public available version of Java (Java 1.0) was released 1995. Over time several version of Java were release which improved and enhanced the language and it libraries. The current version of Java is Java 1.6 also known as Java 6.0. Java is a de facto standard that is controlled through a standard process, called the Java Community Process.

From the Java programming language the Java platform evolved. The Java platform allows that Code is written in other languages then the Java programming language and still runs on the Java virtual machine.

The Java programming language consists out of a Java compiler, the Java virtual machine, and the Java class libraries. The Java virtual machine (JVM) is a software implementation of a computer that executes programs like a real machine.

The Java compiler translates Java coding into so-called byte-code. The Java virtual machine interprets this byte-code and runs the program.

The Java virtual machine is written specifically for a specific operating system.

The Java runtime environment (JRE) consists of the JVM and the Java class libraries.

The target of Java is to write a program once and then run this program on multiple operating systems.

Java has the following properties:

The Java syntax is similar to C++. Java is case sensitive, e.g. the variables myValue and myvalue will be treated as different variables.

The programmer writes java source code which can be done in any text editor which supports plain text as output. Normally the programmer uses an IDE (integrated development environment) for programming. An IDE support usually the programmer in his tasks, e.g. it provides auto-formatting of the source code, highlighting of the important keywords, etc.

At some point the programmer (or the IDE) calls the java compiler. The java compiler creates platform independent code which is called bytecode.

Bytecode can be executed by the java runtime environment. The java runtime environment (JRE) is a program which knows how to run the bytecode on the operating system. The JRE translates the bytecode into native code, e.g. the native code for Linux is different then the native code for Windows and executes it.

The classpath is the connection between the Java compiler and Java interpreter. It defines where the compiler and interpreter look for .class files to load.

By default, the compiler puts each class file in the same directory as its source file. You can specify a separate destination directory with -d

The following Java program is developed under Microsoft Windows. The process on other operating system should be similar but will not be covered here. Select a directory which should contain your code. I will use the directory c:\temp\java which I will as of now call javadir.

Open a text editor which supports plain text, e.g. notepad under Windows and write the following source code. You can start notepad via Start->Run-> notepad and pressing enter.

				
// The smallest Java program possible
public class HelloWorld {
	public static void main(String[] args) {
		System.out.println("Hello World");
	}
}

			

Save the source code in your directory javadir under the name "HelloWorld.java".

Switch to the command line, e.g. under Windows Start-> Run -> cmd. Switch to the javadir directory with the command cd javadir, for example in my case cd c:\temp\java. Use the command dir to see that the source file is in the directory.

Type javac HelloWorld.java .

Check the content of the directory with the command "dir". The directory contains now a file "HelloWorld.class".

Congratulations you compiled your first java source code.

Switch again to the command line, e.g. under Windows Start-> Run -> cmd. Switch to the directory jardir.

Type java HelloWorld .

The system should write "Hello World" on the command line.

You can use the classpath to run the program from another place in your directory.

Switch to the command line, e.g. under Windows Start-> Run -> cmd. Switch to any directory you want.

Type java HelloWorld .

If you are not in the directory in which the compiled class is stored then the system should result an error message Exception in thread "main" java.lang.NoClassDefFoundError: test/TestClass

Type java -classpath "mydirectory" HelloWorld . Replace "mydirectory" with the directory which contains the test directory. You should again see the "HelloWorld" output.

The following will use Eclipse as a development environment. See Using Eclipse as IDE - Tutorial for an introduction on how to use the Eclipse IDE. See Create your first Java program under Eclipse for creating a simple Java project.

Create a new Java project "JavaIntroductionUI".

Create the following class MyFirstUI.java in package ui.

				
package ui;

import java.awt.BorderLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JCheckBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class MyFirstUI extends JFrame {

	private JCheckBox checkbox;
	private JTextField firstName;
	private JTextField lastName;

	public MyFirstUI() {

		// Lets make it look nice
		// This you can ignore / delete if you don't like it
		// try {
		// for (LookAndFeelInfo info : UIManager.getInstalledLookAndFeels()) {
		// if ("Nimbus".equals(info.getName())) {
		// UIManager.setLookAndFeel(info.getClassName());
		// break;
		// }
		// }
		// } catch (Exception e) {
		// e.printStackTrace();
		// }

		setTitle("My First UI");

		// We create a panel which will hold the UI components
		JPanel pane = new JPanel(new BorderLayout());
		// We always have two UI elements (columns) and we have three rows
		int numberOfRows = 3;
		int numberOfColumns = 2;
		pane.setLayout(new GridLayout(numberOfRows, numberOfColumns));

		// create and attach buttons
		// create a label and add it to the main window
		JLabel firstNamelabel = new JLabel(" Firstname: ");
		pane.add(firstNamelabel);
		firstName = new JTextField();
		pane.add(firstName);

		JLabel lastNamelabel = new JLabel(" Lastname: ");
		pane.add(lastNamelabel);
		lastName = new JTextField();
		pane.add(lastName);

		JButton sayHello = new JButton("Say something");
		pane.add(sayHello);

		checkbox = new JCheckBox("Nice");
		pane.add(checkbox);

		// Add the pane to the main window
		getContentPane().add(pane);

		// Pack will make the size of window fitting to the compoents
		// You could also use for example setSize(300, 400);
		pack();

		// Set a tooltip for the button
		sayHello
				.setToolTipText("This button will say something really nice of something bad");
		// sayHello need to do something
		sayHello.addActionListener(new MyActionListener());
	}

	private class MyActionListener implements ActionListener {
		public void actionPerformed(ActionEvent e) {
			if (!checkbox.isSelected()) {
				JOptionPane.showMessageDialog(null, "I don't like you, "
						+ firstName.getText() + " " + lastName.getText() + "!");
			} else {
				JOptionPane.showMessageDialog(null, "How are you, "
						+ firstName.getText() + " " + lastName.getText() + "?");
			}
		}

	}
}

			

Create also the following class MainTester.java in package test and start this class.

				
package test;

import ui.MyFirstUI;

public class MainTester {
	public static void main(String[] args) {
		MyFirstUI view = new MyFirstUI();
		view.setVisible(true);
	}
}

			

You should see the following. A mesage dialog should be seen if you press the button.

In general a general manipulation of an object's variables by other objects or classes is discouraged to ensure data encapsulation. A class should provide methods through which other objects could access variables. Java deletes objects which are not longer used (garbage collection).

Java support the abstraction of data definition and concrete usage of this definition.

The concept is divided from the concrete which means you first define a class containing the variables and the behavior (methods) and afterwards you create the real objects which then all behave like the class defined it.

A class is the definition of the behavior and data. A class can not be directly be used.

A object in an instance of this class and is the real object which can be worked with.

The ability of object variables to contain objects of different classes. If class X1 is a subclass of class X then a method which is defined with a parameter for an object X can also get called which an object X1.

If you define a supertype for a group of classes any subclass of that supertype can be substituted where the supertype is expected.

If you use an interface as a polymorphic type any object which implements this interface can be used as arguments.

Inheritance allows that classes can be based on each other. If a class A inherits another class B this is called "class A extends class B".

For example you can define a base class which provides certain logging functionality and this class is extended by another class which adds email notification to the functionality.

Within java an interface is a type just as a class is a type. Like a class an interface defines methods.

Interfaces are contracts for what a class can do but they say nothing about the way in which the class must do it.

Interfaces are per default public and abstract – explicit declaration of these modifiers is optional.

An interface can also have abstract methods, no concrete methods are allowed.

Interfaces can have constants which are always implicitly public, static and final.

Use == to compare two primitives or to see if two references refers to the same object. Use the equals() method to see if two different objects are equal.

&& and || are both Short Circuit Methods which means that they terminate once the result of an evaluation is already clear. Example (true || .... ) is always true while (false && ...) always false is. Usage:

(var !=null && var.method1()..) ensures that var is not null before doing the real check.

The switch statement can be used to handle several alternatives if they are based on the same constant value.

				
switch (expression) { 
	case constant1: 
		command; 
		break; // Will prevent that the other cases or also executed
	case constant2:
		command; 
		break;
		... 
	default: 
}

Example:

switch (cat.getLevel()) {
			case 0:
				return true;
			case 1:
				if (cat.getLevel() == 1) {
					if (cat.getName().equalsIgnoreCase(req.getCategory())) {
						return true;
					}
				}
			case 2:
				if (cat.getName().equalsIgnoreCase(req.getSubCategory())) {
					return true;
				}
			}
			

The java package java.io contains classes which can be used to read and write to files and other sources. In general the classes in this package can be divided into the following classes:

The following class "MyFile" contains methods for reading and writing a text file.

				
package test;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class MyFile
{

	public String readTextFile(String fileName)
	{
		String returnValue = "";
		FileReader file;
		String line = "";
		try
		{
			file = new FileReader(fileName);
			BufferedReader reader = new BufferedReader(file);
			while ((line = reader.readLine()) != null)
			{
				returnValue += line + "\n";
			}
		} catch (FileNotFoundException e)
		{
			throw new RuntimeException("File not found");
		} catch (IOException e)
		{
			throw new RuntimeException("IO Error occured");
		}
		return returnValue;

	}

	public void writeTextFile(String fileName, String s)
	{
		FileWriter output;
		try
		{
			output = new FileWriter(fileName);
			BufferedWriter writer = new BufferedWriter(output);
			writer.write(s);
		} catch (IOException e)
		{
			e.printStackTrace();
		}

	}
}

			

Use the following to convert from other types to Strings

					
// Convert from int to String
String s1 = String.valueOf ( 10 ); // "10" String s2 =
// Convert from double to String
String.valueOf ( Math.PI ); // "3.141592653589793"
// Convert from boolean to String
String s3 = String.valueOf ( 1 < 2 ); // "true" 
// Convert from date to String
String s4 = String.valueOf ( new Date() ); // "Tue Jun 03 14:40:38 CEST 2003"
			

				
// Conversion from String to int
int i = Integer.parseInt(String);
// Conversion from float to int
float f = Float.parseFloat(String);
// Conversion from double to int
double d = Double.parseDouble(String); 
			

The conversion from string to number is independent from the Locale settings, e.g. it is always using the English notification for number. In this notification a correct number format is "8.20". The German number "8,20" would result in an error.

To convert from a German number you have to use the NumberFormat class. The challenges is that if the value is for example 98.00 then the NumberFormat class would create a Long which cannot be casted to Double. Hence the following complex conversion class.

				
private Double convertStringToDouble(String s) {

		Locale l = new Locale("de", "DE");
		Locale.setDefault(l);
		NumberFormat nf = NumberFormat.getInstance();
		Double result = 0.0;
		try {
			if (Class.forName("java.lang.Long").isInstance(nf.parse(s))) {
				result = Double.parseDouble(String.valueOf(nf.parse(s)));
			} else {
				result = (Double) nf.parse(new String(s));
			}
		} catch (ClassNotFoundException e1) {
			e1.printStackTrace();
		} catch (ParseException e1) {
			e1.printStackTrace();
		}
		return result;
	}
			

int i = (int) double;

Use the following to convert a Date to a SQL date

				
package test;

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;

public class ConvertDateToSQLDate {

private void convertDateToSQL(){
	 SimpleDateFormat template = 
			new SimpleDateFormat("yyyy-MM-dd"); 
		  java.util.Date enddate = 
			new java.util.Date("10/31/99"); 
		  java.sql.Date sqlDate = 
			java.sql.Date.valueOf(
			                template.format(enddate)); 
	 
}
	public static void main(String[] args) {
		ConvertDateToSQLDate date = new ConvertDateToSQLDate();
		date.convertDateToSQL();
	}	 

}

			

A JAR file is a Java Archive based on the pkzip file format. A jar files can contain java classes and other resources (icons, property files) and can be executable.

JAR files are the deployment format for Java. You can distribute your program in a jar file or you can use exiting java code via jars by putting them into your classpath.

An executable JAR means the end-user doesn't have to pull the class files out before running the program. This is done via a manifest.txt file which tells the JVM which class has the main() method. The content of the manifest.txt file:

 Manifest-Version: 1.0 Main-Class: MyApp Class-Path:
				. lib/jcommon-1.0.6.jar lib/itext-1.4.6.jar "Empty Line"
			

A empty line is required otherwise the jar will be executable. Space after a new line is also required

To create one executable JAR file run on the command line

 jar -cvmf mainfest.txt app1.jar *.class
			

While programming Java you have to create several classes, methods, instance variables. The following uses the package test.

										
package test;

public class MyNewClass {

}

									

										
package test;

public class MyNewClass {
	private String var1;
}

									

										
package test;

public class MyNewClass {
	private String var1;

	public MyNewClass(String para1) {
		var1 = para1;
		// or this.var1= para1;
	}
}

									

										
package test;

public class MyNewClass {
	private String var1;

	public MyNewClass(String para1) {
		var1 = para1;
		// or this.var1= para1;
	}

	public void doSomeThing() {

	}

}
									

										
package test;

public class MyNewClass {
	private String var1;

	public MyNewClass(String para1) {
		var1 = para1;
		// or this.var1= para1;
	}

	public void doSomeThing() {

	}

	public void doSomeThing2(int a, Person person) {

	}

}
									

										
package test;

public class MyNewClass {
	private String var1;

	public MyNewClass(String para1) {
		var1 = para1;
		// or this.var1= para1;
	}

	public void doSomeThing() {

	}

	public void doSomeThing2(int a, Person person) {

	}

	public int doSomeThing3(String a, String b, Person person) {
		return 5; // Any value will do for this example
	}

}

									

										
package test;

public class MyOtherClass {
	String myvalue;
	Dog dog;

	public String getMyvalue() {
		return myvalue;
	}

	public void setMyvalue(String myvalue) {
		this.myvalue = myvalue;
	}

	public Dog getDog() {
		return dog;
	}

	public void setDog(Dog dog) {
		this.dog = dog;
	}
}

									

A local variable must always be declared in a method.

Remember the class names should always start with a large letter, e.g. class Test

Remember that variable names should always start with a small letter, e.g. int zahl.

Activate the automatic source code formating at save. Select Windows -> Preferences. Select then Java -> Editor -> Save Actions and make the following settings.

Task: Create two classes. Use basis string concatenation, use the for loop.

Create the package "exercises.exercise02". Create a class "Person" with the following code.

				
package exercises.exercise04;

class Person {
	String firstname = "Jim";
	String lastname = "Knopf";
	int age = 12;

	void writeName() {
		System.out.println(firstname + " " + lastname + "" + age);
	}

}

			

Create a class "Main" with the following source code.

				
package exercises.exercise04;

public class Main {
	public static void main(String[] args) {
		Person person = new Person();
		person.writeName();
	}
}

			

Tasks / Questions:

Task: Develop a constructor for your Person class.

Create the package "exercises.exercise06". Copy your class "Person" to this package and create a constructor

				
package exercises.exercise06;

class Person {
	int age = 12;
	String firstName;
	String lastName;

	public Person(String a, String b) {
		firstName = a;
		lastName = b;
	}

	void writeName() {
		System.out.println(firstName + " " + lastName + "" + age);
	}
}

			

Create another class Main and create two person.

				
package exercises.exercise06;

public class Main {
	public static void main(String[] args) {
		Person person = new Person("Jim", "Knopf");
		person.writeName();
		Person person = new Person("Henry", "Ford");
		person.writeName();
	}
}

			

Create package exercises.exercise08.

Write a Class "Math" which performs the following:

Write a class Main which tests each method and writes the result to the console. The test class could look like the following.

				
package exercises.exercise08;

public class Main {
	public static void main(String[] args) {
		Math math = new Math();
		System.out.println(math.multiply(5, 2));
		System.out.println(math.add(8, 2));
		System.out.println(math.substact(5, 2));
		System.out.println(math.divide(5, 2));
	}
}

			

Task: Develop a constructor for your Person class.

Create the package "exercises.exercise10". Create a class "Person" with the following code.

				
package exercises.exercise10;

public class Person {
	// We define two variables for the first and last name
	// String is the type of the variable
	private String firstName;
	private String lastName;

	// This is the constructor of the class it expects two variables:
	// firstName
	// lastName
	public Person(String firstName, String lastName) {
		// the keyword "this" allows to refer to variables of the class.
		// It allows to distinguish between the variables which are passed
		// into the constructor and the variables of the class
		this.firstName = firstName;
		this.lastName = lastName;
	}

	public void setFirstName(String s) {
		firstName = s;
	}

	public void setLastName(String s) {
		lastName = s;
	}

	public String getFirstName() {
		return firstName;
	}

	public String getLastName() {
		return lastName;
	}
}

			

Create a class "Main" with the following source code.

				
package exercises.exercise10;

// This class defines the main method and nothing else
// The "real" object is person
public final class Main {
	private Main() {
	}

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		Person person = new Person("Jim", "Knopf");
		Person person2 = new Person("Jill", "Sanders"");
		// Jill heiratet Jim
		person2.setLastName("Knopf");
		
	}
}

			

Task: Create an address class with the following fields:

Write setter and getter for the address. Each person should have an address. Add a field "address" to the person.

Task: We want to calculate the alcohol concentration of a person. Create an Beer class with the following fields:

Write setter and getter for both fields. Write a method which calculates the quantity of alcohol in a beer based on the following formula: Quantity * 0,8 (fixed factor for the density of alcohol) * PercentageAlcohol

As of now you should have created a Person class and a Address class. This exercise tries to ensure that everyone has a simular solution.

Create a new package exercises.exercise16

Copy to / re-create your class Person in the package exercises.exercise16. This class should be similar to to following code:

		
package exercises.exercise16;

public class Address {

	private String street;
	private String number;
	private String postalCode;
	private String city;
	private String country;

	public String getStreet() {
		return street;
	}

	public void setStreet(String street) {
		this.street = street;
	}

	public String getNumber() {
		return number;
	}

	public void setNumber(String number) {
		this.number = number;
	}

	public String getPostalCode() {
		return postalCode;
	}

	public void setPostalCode(String postalCode) {
		this.postalCode = postalCode;
	}

	public String getCity() {
		return city;
	}

	public void setCity(String city) {
		this.city = city;
	}

	public String getCountry() {
		return country;
	}

	public void setCountry(String country) {
		this.country = country;
	}

	public String toString() {
		return street + " " + number + " " + postalCode + " " + city + " "
				+ country;
	}

}

	

		
package exercises.exercise16;

public class Person {
	private String firstName;
	private String lastName;
	private int age;
	private Address address;

	// Constructor
	public Person(String firstName, String lastName) {
		this.firstName = firstName;
		this.lastName = lastName;
	}

	public String getFirstName() {
		return firstName;
	}

	public void setFirstName(String firstName) {
		this.firstName = firstName;
	}

	public String getLastName() {
		return lastName;
	}

	public void setLastName(String lastName) {
		this.lastName = lastName;
	}

	public int getAge() {
		return age;
	}

	public void setAge(int age) {
		this.age = age;
	}

	public Address getAddress() {
		return address;
	}

	public void setAddress(Address address) {
		this.address = address;
	}

	public String toString() {
		return firstName + " " + lastName + " " + age;
	}
}

	

Create a new class Tester with a main method which will use the created classes.

		
package exercises.exercise16;

public class Tester {

	public static void main(String[] args) {
		// I create a person
		Person pers = new Person("Jim", "Knopf");
		// I set the age of the person to 32
		pers.setAge(32);

		// Just for testing I write this to the console
		System.out.println(pers.toString());
		/*
		 * Actually System.out.println calls always toString, if you don't
		 * specify it so you could also have written System.out.println(pers);
		 */
		// I create an address
		Address address = new Address();
		// I set the values for the address
		address.setCity("Heidelberg");
		address.setCountry("Germany");
		address.setNumber("104");
		address.setPostalCode("69214");
		address.setStreet("Musterstr.");

		// I assign the address to the person
		pers.setAddress(address);

		// I don't need address any more
		address = null;

		// person is moving to the next house in the same street
		pers.getAddress().setNumber("105");

	}

}

	

Task: Write a main program which creates a random number between 0 - 100 and asked the user if the number is higher then 50 or less then 50. If the user did ask right then write "Very well, you did it!" to the console, otherwise write "You are a loooooser!" to the console.

Create package exercise20 for this exercise.

Create the following class. This is a helper class you will use for reading input from the command line.

		
package exercises.exercise20;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

/*
 * This class will read an line from the command line
 * and return it from the caller
 */
public class ReadInput {
	public String readLine() {
		InputStreamReader converter = new InputStreamReader(System.in);
		BufferedReader in = new BufferedReader(converter);
		// We will later learn want a try / catch block is
		try {
			String userInput = in.readLine();
			return userInput;
		} catch (IOException e) {
			e.printStackTrace();
			return "failed";
		}
	}
}

	

Copy the program from below and try to understand if statement if part of it.

		
package exercises.exercise20;

// We will later learn want a import mean
import java.util.Random;

public class Main {
	public static void main(String[] args) {
		String userInput = "";
		Random random = new Random();
		// Create a number between 0 and 100
		int nextInt = random.nextInt(101);
		ReadInput in = new ReadInput();
		System.out.println("Do you think the number is larger then 50?");
		userInput = in.readLine();
		if (userInput.equalsIgnoreCase("y") && nextInt > 50) {
			System.out.println("Very well, you did it!");
		} else {
			System.out.println("You are a loooooser!");
		}
		System.out.println("The number was " + nextInt);
	}
}

	

Task: Write a main program which creates a random number between 0 - 100. The user must guess the number until we has found the correct answer.

Create package exercise22 for this exercise.

This is a helper class for reading has been improve to read an integer from the command line. Use this class. Your task is then to write the main method for the game.

		
package exercises.exercise22;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

/*
 * This class will read an line from the command line
 * and return it from the caller
 */
public class ReadInput {
	public String readLine() {
		InputStreamReader converter = new InputStreamReader(System.in);
		BufferedReader in = new BufferedReader(converter);
		// We will later learn want a try / catch block is
		try {
			String userInput = in.readLine();
			return userInput;
		} catch (IOException e) {
			e.printStackTrace();
			return "failed";
		}
	}

	public int readInteger() {
		String in = readLine();
		try {
			// Translate string to integer
			return Integer.parseInt(in);
		} catch (NumberFormatException e) {
			// In case we did not get a number return zero
			return 0;
		}

	}
}

	

Task: Create a class TestArray with declares an array which can store 2 persons. Store 2 persons in this array and use a for loop to write the first name to the console.

		
package exercises.exercise24;

public class TestArray {
	public static void main(String[] args) {
		Person personArray[] = new Person[2];
		Person person = new Person("Lars", "Vogel");
		personArray[0] = person;
		person = new Person("Jim", "Knopf");
		personArray[1] = person;

		for (int i = 0; i < personArray.length; i++) {
			// Print the first name of the person
			System.out.println(personArray[i].getFirstName());
		}
	}
}

	

Task: Read a text file which contains a list of persons. Use an editor for this which does save the information as plain text, e.g. notepad.

For example the file might look like:

			
Lars,Vogel
Jim,Knopf
Hendrik,Test

		

Save it on your file system, e.g. on c:\temp\person.txt

Use the class from the following description: Reading and Write to text Files.

			
MyFile file = new MyFile();
file.readTextFile("c:/temp/person.txt");
file.readTextFile("c:\\temp\\person.txt");

		

Write a main program which reads this file and writes the content to the console.

Extent your example from exercise 26 so that the first name and the last name a written into a separate line.

Extent your example from exercise 28 so that new object of type Person is created for each line. Save all persons in an array or in an ArrayList. Print to the console the total number of all persons.

Extent exercise 30. Loop over your array and find out if you have a person in your ArrayList / array where the first name starts with J and the last name starts with K.

Task: Write a program which calculates the tax for a person based on the german system.

Create package exercise30 for this exercise. Copy your Person and Address class into this package.

Extend your Person class so that a person has also an income field. Create setter and getter for this field.

The German income tax is calculated the following (see wikipedia):

Task: Write a class TaxCalculator with the following method: public float calculateTax(Person person). This method should calculate the tax for a give person. Write also a main method which tests this class.

Task: Understand automatic memory management.

Java provides automatic memory management. This does not mean that you have infinite memory. Java will release all memory which is not used anymore but the Java application will crash if you request more memory from the system then is available for the Java application.

Create the package "exercises.exercise20" and the following classes. Check if you get an out-of-memory situation.

				
package exercises.exercise20;

public class MinMax {
	private int min = 0;
	private int max = 0;

	public int getMin() {
		return min;
	}

	public void setMin(int min) {
		this.min = min;
	}

	public int getMax() {
		return max;
	}

	public void setMax(int max) {
		this.max = max;
	}

}

			

				
package exercises.exercise20;

import java.util.ArrayList;

public class TestCreateObjects {
	private static final long MAX = 10000000;

	public void create() {
		System.out.println("First only the objects");
		for (long i = 0; i <= MAX; i++) {
			MinMax object = new MinMax();
			object.setMin(100);
			object.setMin(200);
			if ((i % 100000) == 0) {
				System.out.println("Number of objects " + i);
			}
		}
	}

	public void createList() {
		System.out.println("Now the list");
		ArrayList<MinMax> list = new ArrayList<MinMax>();
		for (long i = 0; i <= MAX; i++) {
			MinMax object = new MinMax();
			object.setMin(100);
			object.setMin(200);
			list.add(object);
			if ((i % 100000) == 0) {
				System.out.println("Number of objects " + i);
			}
		}
	}
}

			

				
package exercises.exercise20;

public final class Main {
	// Avoid that someone creates an instance of this class
	private Main() {
	}

	/**
	 * @param args
	 */
	// This will
	public static void main(String[] args) {
		TestCreateObjects test = new TestCreateObjects();
		// Will we get a out-of-memory error?
		test.create();
		// Will we get a out-of-memory error?
		test.createList();
	}
}