Java Basic(58)-Abstract and Concrete Classes

abstract public class food { →但類必須是abstract的

public abstract void eat(); → 你可以有abstract方法

}

In sub-class:

public class tuna extends food{

public void eat(){ →必須是 public

System.out.println("this tuna is great");

}

}

public class potpie extends food{

public void eat(){ →必須是 public

System.out.println("this potpie is great");

}

}

在子類必須定方法，因為它們是extends從super-class（food）

Java Basic(57)-Overriding Rules

1.food是main class(super-class)，和potpie和tuna是子類(sub-class)

2.potpie和tuna不能有不同的參數 ，必須是相同的在super class（food）

3.abstract public class food {

void eat(){

System.out.println("this food is great");

}

}

abstract 意味著你不能創建對象在fatty.class或apples.class

Java Basic(56)-Polymorphic Arguments

創建新class稱為fatty：

public class fatty {

public void digest(food x){ →方法稱為digest和food X為參數

x.eat();

}

}

in apples.java:

class apples{

public static void main(String[] args){

fatty bucky = new fatty();

food fo = new food(); →因為在fatty.class，參數是food

food po = new tuna(); →您可以調用在potpie和tuna的價值

bucky.digest(fo);

bucky.digest(po);

}

}

這是運行時的結果： 

this food is great

this tuna is great

Java Basic(55)-Introduction to Polymorphism

public class food {

void eat(){

System.out.println("this food is great");

}

}

public class potpie extends food{

void eat(){

System.out.println("this potpie is great");

}

}

public class tuna extends food{

void eat(){

System.out.println("this tuna is great");

}

}

class apples{

public static void main(String[] args){

food bucky[]=new food[2]; → 陣列

bucky[0]=new potpie(); → 這裡的新對象

bucky[1]=new tuna(); → 這裡的新對象

for(int x=0;x<2;++x){

bucky[x].eat();

}

}

}

由於potpie和tuna extends到food，你不需要為tuna.tunaObject（類似的東西

這是運行時的結果： 

this potpie is great

this tuna is great

Java Basic(54)-Event Handler Program

import java.awt.FlowLayout;

import java.awt.event.ActionListener;

import java.awt.event.ActionEvent;

import javax.swing.JFrame; →導入你必須需要什麼

import javax.swing.JTextField;

import javax.swing.JPasswordField;

import javax.swing.JOptionPane;

public class tuna extends JFrame{

private JTextField item1;

private JTextField item2; →三個TextField和passwordField

private JTextField item3;

private JPasswordField passwordField;

public tuna(){

super("The title");

setLayout(new FlowLayout());

item1 = new JTextField(10); →設置項目（constructor）

add(item1);

item2 = new JTextField("enter text here");

add(item2);

item3 = new JTextField("uneditable");

item3.setEditable(false);

add(item3);

passwordField = new JPasswordField("mypass");

add(passwordField);

thehandler handler = new thehandler(); →創建新對象

item1.addActionListener(handler); →設置處理程序(handler)

item2.addActionListener(handler);

item3.addActionListener(handler);

passwordField.addActionListener(handler);

}

private class thehandler implements ActionListener{ →必須這樣寫

public void actionPerformed(ActionEvent event){

String string = "";

if(event.getSource()==item1)

string=String.format("field 1: %s", event.getActionCommand());

else if(event.getSource()==item2)

string=String.format("field 2: %s", event.getActionCommand());

else if(event.getSource()==item3)

string=String.format("field 3: %s", event.getActionCommand());

else if(event.getSource()==passwordField)

string=String.format("password field is: %s" , event.getActionCommand());

JOptionPane.showMessageDialog(null, string); →顯示文字在TextField

}

}

}

import javax.swing.JFrame;

class apples{

public static void main(String[] args){

tuna bucky = new tuna();

bucky.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

bucky.setSize(350, 100);

bucky.setVisible(true);

}

這是運行時的結果： 

}

Java Basic(53)-ActionListener

import java.awt.FlowLayout;

import java.awt.event.ActionListener;

import java.awt.event.ActionEvent;

import javax.swing.JFrame;

import javax.swing.JTextField;

import javax.swing.JPasswordField;

import javax.swing.JOptionPane;

public class tuna extends JFrame{

private JTextField item1;

private JTextField item2;

private JTextField item3;

private JPasswordField passwordField;

public tuna(){

super("The title");

setLayout(new FlowLayout());

item1 = new JTextField(10);

add(item1);

item2 = new JTextField("enter text here");

add(item2);

item3 = new JTextField("uneditable");

item3.setEditable(false);

add(item3);

passwordField = new JPasswordField("mypass");

add(passwordField);

thehandler handler = new thehandler();

item1.addActionListener(handler);

item2.addActionListener(handler);

item3.addActionListener(handler);

passwordField.addActionListener(handler);

}

private class thehandler implements ActionListener{

public void actionPerformed(ActionEvent event){

String string = "";

if(event.getSource()==item1)

string=String.format("field 1: %s", event.getActionCommand());

else if(event.getSource()==item2)

string=String.format("field 2: %s", event.getActionCommand());

else if(event.getSource()==item3)

string=String.format("field 3: %s", event.getActionCommand());

else if(event.getSource()==passwordField)

string=String.format("password field is: %s" , event.getActionCommand());

}

}

}