Taqi Shah Blogspot

A command line executing the java command, which in turn executes a Java main program.

    java MyProgram param1 param2 param3

public class MyProgram {

  public static void main(String[] args) {

    System.out.println("Hello World, Java Program");

  }
}

    System.out.println("Hello World, Java Program");

• private
• default
• protected
• public

private

public class Clock {
    private long time = 0;
}

public class Clock {
    private long time = 0;

    public long getTime() {
        return this.time;
    }

    public void setTime(long theTime) {
        this.time = theTime;
    }
}

default

public class Clock {
    long time = 0;
}


public class ClockReader {
    Clock clock = new Clock();

    public long readClock{
        return clock.time;
    }
}

protected

public class Clock {
    protected long time = 0;    // time in milliseconds
}


public class SmartClock() extends Clock{

    public long getTimeInSeconds() {
        return this.time / 1000;
    }
}

public

public class Clock {
    public long time = 0;
}


public class ClockReader {
    Clock clock = new Clock();

    public long readClock{
        return clock.time;
    }
}

An example Java package structure.

com.jenkov.navigation

com.jenkov.navigation.Page

Putting Classes into Packages

1. Put the Java class inside a directory matching the package you want to put the class in.
2. Declare that class as part of the package.

package com.jenkov.navigation;

public class Page {
    ...
}

Package Naming Conventions

• Defining a Constructor
• Multiple Constructors
• Calling a Constructor
• Constructor Parameters
• Access Modifier
• Default, no-arg Constructor

Defining a Constructor

public class MyClass {

    public MyClass() {

    }
}

    public MyClass() {

    }

Multiple Constructors

Calling a Constructor

MyClass myClassVar = new MyClass();

MyClass myClassVar = new MyClass("John", "Doe", 1975);

Constructor Parameters

public class Employee {

    private String firstName = null;
    private String lastName  = null;
    private int    birthYear = 0;


    
    public Employee(String first,
                    String last,
                    int    year   ) {

        firstName = first;
        lastName  = last;
        birthYear = year;
    }
    

}

    public Employee(String first, String last, int year ) {
        firstName = first;
        lastName  = last;
        birthYear = year;
    }
    

Employee employee = new Employee("Jack", "Daniels", 2000);

Access Modifier

Default, no-arg Constructor