exception測試2

class BadFoodException extends Exception{ }
public class MyException{
    static String[] food = {"Apple", "Banana", "Cocoa", "Coffee", "Toast"};

    public static void main(String[] args){
        try{
            checkFood(args[0]);
        }catch(BadFoodException e){
            System.out.println("I don't like.");
        }
    }
   
    static void checkFood(String input) throws BadFoodException{
        int flag = 0;
        for(String s : food){
            if(s.equals(input)){
                flag = 1;
                break;
            }
        }
        if(flag == 1)    System.out.println("I like it.");
        else throw new BadFoodException();
    }
}



==================================
$ java MyException Toast
I don't like.

$ java MyException Apple
I like it.

exception測試

class Propagate{
    public static void main(String[] args){
        try{
            System.out.println(new Propagate().reverse(""));
        }catch(ArithmeticException e){
            System.out.println("Input error!");
        }finally{
            System.out.println("The main method is done.");
        }
    }
   
    String reverse(String s){
        String reverseStr = "";
       
        if(s.length() == 0)    throw new ArithmeticException();
        else{
            for(int i=s.length()-1; i>=0; --i){
                reverseStr += s.charAt(i);
            }
        }
        return reverseStr;
    }
}



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reverse("Hello")
olleH
The main method is done.


reverse("")
Input error!
The main method is done.

例外是隨便挑一個做throw

列舉多載method

public class Bridge{
    public enum Suits{
        CLUBE(20), DIAMONDS(20), HEARTS(30), SPADES(30),
        NOTRUMP(40){
            public int getValue(int bid){
                return (bid - 1) * 30 + 40;
            }
        };
       
        Suits(int points){
            this.points = points;
        }
       
        private int points;
       
        public int getValue(int bid){
            return points * bid;
        }
    }
   
    public static void main(String[] args){
        System.out.println(Suits.NOTRUMP.getValue(3));
        System.out.println(Suits.SPADES + " " + Suits.SPADES.points);
        System.out.println(Suits.values());
    }
}



=========================
100
SPADES 30
[LBridge$Suits;@4a65e0

instanceof測試

class Animal{
    public void testIsA(Animal a){
        System.out.println("Animal");
    }
}
class Dog extends Animal{
    public void testIsA(Animal a){    //a是Animal的參考
        System.out.println(a instanceof Animal);    //但instanceof會看a的物件型別
        System.out.println(a instanceof Dog);
        //a.show();            //此行會產生錯誤，因為a的型別為Animal，而該class無show函式
    }
    public void show(){
        System.out.println("I am class Dog");
    }
}

public class InstanceOfTest{
    public static void main(String[] args){
        Animal dog1 = new Animal();
        Animal dog2 = new Dog();
        Dog dog3 = new Dog();
       
        System.out.println(dog1 instanceof Animal);        //true; Animal IS-A Animal
        System.out.println(dog1 instanceof Dog);        //false; Animal IS-A Dog
        System.out.println(dog2 instanceof Animal);        //true; Dog IS-A Animal
        System.out.println(dog2 instanceof Dog);        //true; Dog IS-A Dog
        System.out.println(dog3 instanceof Animal);        //true; Dog IS-A Dog
       
        dog1.testIsA(dog1);        //Animal,*****
        dog1.testIsA(dog2);        //Animal,overriding取決於呼叫的物件
        dog1.testIsA(dog3);        //Animal,*****
       
        dog1.testIsA(dog1);        //Animal,overriding取決於呼叫的物件
        dog2.testIsA(dog2);        //true, Dog IS-A Animal
                                //true, Dog IS-A Dog
        dog3.testIsA(dog3);        //true,true,
    }
}

＝＝＝＝＝＝
結論：
1・父類別物件可以呼叫子類別函式（通常父類別看不見子類別內的成員），但只限於被子類別overriding過的函式。
2・不管傳入函式的引數為何，皆以函式之參數的型別宣告為準。
3・而instanceof會去看參考所指向的物件，並以該物件為準。

父類別函式覆寫

 父類別參考指向子類別物件，執行被覆寫之函式

class GameShape{
    public void display(){
        System.out.println("GameShape");
    }
    public void motion(){
        System.out.println("Motion");
    }
}

public class Player1 extends GameShape{
    public void display(){
        System.out.println("Player1");
    }
    public void show(){
        System.out.println("show");
    }
    public void showDad(){
        super.display();
    }
   
    public static void main(String[] args){
        GameShape game = new Player1();
        Player1 player = new Player1();
       
        game.display();
        player.display();
       
        game.motion();
        player.motion();
       
        player.showDad();
        player.show();
    }
}














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Player1
Player1
Motion
Motion
GameShape
show

111106_運算式

1.1+2*3+(4+5*6)/(9-7) 2.1*2+3*(4+5)

括號：((1+(2*3))+((4+5*6)/(9-7))) 括號：((1*2)+(3*(4+5)))

前：++1*23/+4*56-97 前：+*12*3+45

後：123*+456*+97-/+ 後：12*345+*+

實作abstract類別

Fruit.java


package food;
public abstract class Fruit{
protected String color;
protected String name;
public void setColor(String str){
color = str;
}
public abstract void show();
}


Apple.java


import food.Fruit;
class Apple extends Fruit{
protected int price;
public Apple(){}
public Apple(int price){
this.price = price;
}
public void setName(String name){
this.name = name;
}
public void setColor(String color){
this.color = color;
}
public void show(){
System.out.println("There is a fruit, it's color is " + color + ",it's an " + name + ".");
System.out.println("And the price of an apple is " + price + ".");
}

public static void main(String[] args){
Apple apple = new Apple(10);
apple.setName("Apple");
apple.setColor("red");
apple.show();
}
}



-------------------------------------------------------------------------

$ java -classpath /Users/superppp/Documents/java Apple

There is a fruit, it's color is red,it's an Apple.

And the price of an apple is 10.