多型性和不同型別的重寫
來自 java 教程
多型性的字典定義是指生物學中的原理,其中生物體或物種可以具有許多不同的形式或階段。這個原則也可以應用於物件導向的程式設計和 Java 語言之類的語言。類的子類可以定義它們自己的唯一行為,但仍然共享父類的一些相同功能。
看看這個例子,瞭解不同型別的覆蓋。
- 基類沒有實現,子類必須覆蓋完整的方法 - (摘要)
- 基類提供預設實現,子類可以改變行為
- 子類通過呼叫
super.methodName()
作為第一個語句來為基類實現新增擴充套件 - 基類定義演算法的結構(模板方法),子類將覆蓋演算法的一部分
程式碼段:
import java.util.HashMap;
abstract class Game implements Runnable{
protected boolean runGame = true;
protected Player player1 = null;
protected Player player2 = null;
protected Player currentPlayer = null;
public Game(){
player1 = new Player("Player 1");
player2 = new Player("Player 2");
currentPlayer = player1;
initializeGame();
}
/* Type 1: Let subclass define own implementation. Base class defines abstract method to force
sub-classes to define implementation
*/
protected abstract void initializeGame();
/* Type 2: Sub-class can change the behaviour. If not, base class behaviour is applicable */
protected void logTimeBetweenMoves(Player player){
System.out.println("Base class: Move Duration: player.PlayerActTime - player.MoveShownTime");
}
/* Type 3: Base class provides implementation. Sub-class can enhance base class implementation by calling
super.methodName() in first line of the child class method and specific implementation later */
protected void logGameStatistics(){
System.out.println("Base class: logGameStatistics:");
}
/* Type 4: Template method: Structure of base class can't be changed but sub-class can some part of behaviour */
protected void runGame() throws Exception{
System.out.println("Base class: Defining the flow for Game:");
while (runGame) {
/*
1. Set current player
2. Get Player Move
*/
validatePlayerMove(currentPlayer);
logTimeBetweenMoves(currentPlayer);
Thread.sleep(500);
setNextPlayer();
}
logGameStatistics();
}
/* sub-part of the template method, which define child class behaviour */
protected abstract void validatePlayerMove(Player p);
protected void setRunGame(boolean status){
this.runGame = status;
}
public void setCurrentPlayer(Player p){
this.currentPlayer = p;
}
public void setNextPlayer(){
if (currentPlayer == player1) {
currentPlayer = player2;
}else{
currentPlayer = player1;
}
}
public void run(){
try{
runGame();
}catch(Exception err){
err.printStackTrace();
}
}
}
class Player{
String name;
Player(String name){
this.name = name;
}
public String getName(){
return name;
}
}
/* Concrete Game implementation */
class Chess extends Game{
public Chess(){
super();
}
public void initializeGame(){
System.out.println("Child class: Initialized Chess game");
}
protected void validatePlayerMove(Player p){
System.out.println("Child class: Validate Chess move:" + p.getName());
}
protected void logGameStatistics(){
super.logGameStatistics();
System.out.println("Child class: Add Chess specific logGameStatistics:");
}
}
class TicTacToe extends Game{
public TicTacToe(){
super();
}
public void initializeGame(){
System.out.println("Child class: Initialized TicTacToe game");
}
protected void validatePlayerMove(Player p){
System.out.println("Child class: Validate TicTacToe move:" + p.getName());
}
}
public class Polymorphism{
public static void main(String args[]){
try{
Game game = new Chess();
Thread t1 = new Thread(game);
t1.start();
Thread.sleep(1000);
game.setRunGame(false);
Thread.sleep(1000);
game = new TicTacToe();
Thread t2 = new Thread(game);
t2.start();
Thread.sleep(1000);
game.setRunGame(false);
}catch(Exception err){
err.printStackTrace();
}
}
}
輸出:
Child class: Initialized Chess game
Base class: Defining the flow for Game:
Child class: Validate Chess move:Player 1
Base class: Move Duration: player.PlayerActTime - player.MoveShownTime
Child class: Validate Chess move:Player 2
Base class: Move Duration: player.PlayerActTime - player.MoveShownTime
Base class: logGameStatistics:
Child class: Add Chess specific logGameStatistics:
Child class: Initialized TicTacToe game
Base class: Defining the flow for Game:
Child class: Validate TicTacToe move:Player 1
Base class: Move Duration: player.PlayerActTime - player.MoveShownTime
Child class: Validate TicTacToe move:Player 2
Base class: Move Duration: player.PlayerActTime - player.MoveShownTime
Base class: logGameStatistics: