Question

我正在学习Java，在书中写的是＃34;如果第一个语句不是对父构造函数的调用，Java编译器会自动插入对无参数构造函数super（）的调用。＆＃34;

但是对于我来说它是不完整的，完整的将是＆＃34;如果第一个语句不是对父构造函数的调用，或者调用，那么Java编译器会自动插入对无参数构造函数super（）的调用。此（）＆＃34; this（）表示类中有或没有参数的任何构造函数，我是对的吗？

我的意思是，在第一种情况下，编译器确实会将super（）添加为第一个语句，但在第二种情况下，对于带有参数的构造函数则不会：

案例1：

public class MyClass{ 
    public MyClass() {}
}

编译后，变为：

public class MyClass { 
    public MyClass() {super();}
}

案例2：

public class MyClass{ 
    public MyClass() {}
    public MyClass(int num) { this(); }
}

编译后，变为：

public class MyClass{ 
    public MyClass() {super();}
    public MyClass(int num) { this(); }
}

Answer 1

你是对的，调用同一个类的另一个构造函数，例如div也是完全有效的。您可以使用import pygame from pygame.locals import* #initialise pygame pygame.init() WHITE = (255,255,255) #counts which sprite you should be on when running #create screen screen_width = 160 screen_height = 144 screen_multiplier = 4 screen = pygame.display.set_mode(((screen_width*screen_multiplier), (screen_height*screen_multiplier))) pygame.display.set_caption('Pokemon Blood Red') #Sprite stuff sprite = pygame.image.load('player_east_still.png') #Reform the sprite sprite = pygame.transform.scale(sprite, (10*screen_multiplier, 14*screen_multiplier)) sprite.set_colorkey(WHITE) ############################################################################# class Player(pygame.sprite.Sprite): def __init__(self): super(Player, self).__init__() self.player_sprite = pygame.Surface((10*screen_multiplier, 14*screen_multiplier)) self.player_sprite.fill(WHITE) self.rect = self.player_sprite.get_rect() self.rect.x = 200 self.rect.y = 200 class Blocks(pygame.sprite.Sprite): def __init__(self): super(Blocks, self).__init__() self.trees = pygame.Surface((10*screen_multiplier, 14*screen_multiplier)) self.trees.fill(WHITE) self.rect = self.trees.get_rect() self.rect.x = 25 self.rect.y = 25 player = Player() blocks = Blocks() pygame.init() amount_caught = 0 place = 1 catch1 = {'pokemon':'none', 'hp':0, 'attack':0, 'defence':0, 'sp_attack':0, 'sp_defence':0,} background = 1 def area_load(): global background if background == 1: background = pygame.image.load('neuory_town.png').convert() background = pygame.transform.scale(background, (160*screen_multiplier, 144*screen_multiplier)) area_load() (x) = 160*0.45 (y) = 144*0.45 def caught(): if amount_caught == 0: pass #catch1 values are equal to wild one's #Mainloop crashed = False while not crashed: x_change = 0 y_change = 0 #Different buttons for event in pygame.event.get(): if event.type == pygame.QUIT: crashed = True pygame.quit() elif event.type == pygame.KEYDOWN: if event.key == pygame.K_LEFT: x_change = -3*screen_multiplier player.rect.x += x_change screen.blit(player.player_sprite, (player.rect.x, player.rect.y)) hits = pygame.sprite.spritecollide(player, blockades, False) if hits: print ('Collision!') x_change = 0 player.rect.x = 10*screen_multiplier + blocks.rect.x sprite = pygame.image.load('player_west_still.png') elif event.key == pygame.K_RIGHT: x_change = 3*screen_multiplier player.rect.x += x_change screen.blit(player.player_sprite, (player.rect.x, player.rect.y)) hits = pygame.sprite.spritecollide(player, blockades, False) if hits: print ('Collision!') x_change = 0 player.rect.x = blocks.rect.x - 10*screen_multiplier sprite = pygame.image.load('player_east_still.png') elif event.key == pygame.K_UP: y_change = -3*screen_multiplier player.rect.y += y_change screen.blit(player.player_sprite, (player.rect.x, player.rect.y)) hits = pygame.sprite.spritecollide(player, blockades, False) if hits: print ('Collision!') y_change = 0 player.rect.y = 14*screen_multiplier + blocks.rect.x sprite = pygame.image.load('player_north_still.png') elif event.key == pygame.K_DOWN: y_change = 3*screen_multiplier player.rect.y += y_change screen.blit(player.player_sprite, (player.rect.x, player.rect.y)) hits = pygame.sprite.spritecollide(player, blockades, False) if hits: print ('Collision!') y_change = 0 player.rect.y = blocks.rect.x - 14*screen_multiplier sprite = pygame.image.load('player_south_still.png') elif event.type == pygame.KEYUP: if event.key == pygame.K_LEFT: x_change = 0 elif event.key == pygame.K_RIGHT: x_change = 0 elif event.key == pygame.K_UP: y_change = 0 elif event.key == pygame.K_DOWN: y_change = 0 x += x_change y += y_change player.rect.x += x_change player.rect.y += y_change blockades = pygame.sprite.Group() blockades.add(blocks) #Check for collisions hits = pygame.sprite.spritecollide(player, blockades, False) #Draw everything sprite = pygame.transform.scale(sprite, (10*screen_multiplier, 14*screen_multiplier)) sprite.set_colorkey(WHITE) screen.blit(player.player_sprite, (player.rect.x, player.rect.y)) screen.blit(blocks.trees, (blocks.rect.x, blocks.rect.y)) screen.blit(background,(0,0)) screen.blit(sprite,(player.rect.x,player.rect.y)) pygame.display.flip() pygame.quit()工具查看Java编译器发出的字节码：

this()

javap构造函数委托给$ javap -c ../MyClass.class Compiled from "MyClass.java" public class MyClass { public MyClass(); Code: 0: aload_0 1: invokespecial #1 // Method java/lang/Object."<init>":()V 4: return public MyClass(int); Code: 0: aload_0 1: invokespecial #2 // Method "<init>":()V 4: return }，后者又调用默认的MyClass(int)构造函数。

澄清继承和构造函数中的Java 8编译器增强

1 个答案: