英文:
How to use graphics 2d in kotlin with paint()
问题
我想开始制作一个2D视频游戏，我在Java中找到了一个教程。然而，我想使用Kotlin，因为我听说它更好，我对Java和Kotlin编程都很新，我需要将这个代码放入：
```kotlin
Graphics2d g2 = Graphics2D(g)
在Kotlin中，我没有找到任何方法通过搜索。
如果你想知道（但我认为这并不重要）JPanel类文件在这里：
import java.awt.Color
import java.awt.Dimension
import java.awt.Graphics
import java.awt.Graphics2D
import javax.swing.JPanel
class GamePanel : JPanel(), Runnable{
//屏幕设置
var originalTileSize = 16
var scale = 3
var tileSize = originalTileSize * scale
var maxScreenCol = 16
var maxScreenRow = 12
var gameThread = Thread()
var screenWidth = maxScreenCol * tileSize // 768
var screenHeight = maxScreenRow * tileSize // 576 TO CHANGE????
init {
this.setPreferredSize(Dimension(screenWidth, screenHeight))
this.setBackground(Color.BLACK)
this.setDoubleBuffered(true)
}
// 游戏线程代码
public fun startGameThread(){
gameThread = Thread(this)
gameThread.start()
}
// 运行游戏循环
public override fun run(){
while (gameThread != null){
update()
repaint()
}
}
public fun update(){
// 现在没有任何内容
}
public override fun paintComponent(g : Graphics) {
super.paintComponent(g)
val g2: Graphics2D = g as Graphics2D
}
}
英文:
I want to start making a 2d video game, and I found a tutorial in java. However I wanted to use kotlin because I heard it is better, I am new to java and kotlin programming and I needed to put this
Graphics2d g2 = Graphics2D(g)
In kotlin, I didn't find anyway by searching.
If you want to know(but I think it doesn't matter) The JPanel class file is here:
import java.awt.Color
import java.awt.Dimension
import java.awt.Graphics
import java.awt.Graphics2D
import javax.swing.JPanel
class GamePanel : JPanel(), Runnable{
//Screen settings
var originalTileSize = 16
var scale = 3
var tileSize = originalTileSize * scale
var maxScreenCol = 16
var maxScreenRow = 12
var gameThread = Thread()
var screenWidth = maxScreenCol * tileSize // 768
var screenHeight = maxScreenRow * tileSize // 576 TO CHANGE????
init {
this.setPreferredSize(Dimension(screenWidth, screenHeight))
this.setBackground(Color.BLACK)
this.setDoubleBuffered(true)
}
// Game Thread code
public fun startGameThread(){
gameThread = Thread(this)
gameThread.start()
}
// run the game loop
public override fun run(){
while (gameThread != null){
update()
repaint()
}
}
public fun update(){
// Nothing for now
}
public override fun paintComponent(g : Graphics) {
super.paintComponent(g)
Graphics2D g2 = Graphics2D(g)
}
}
</details>
# 答案1
**得分**: 1
在Kotlin中，使用`as`关键字执行类型转换，如下所示：
```kotlin
val g2 = g as Graphics2D
您还可以使用安全转换操作符as?，如果转换不可行，它会返回null，而不是抛出异常：
override fun paintComponent(g: Graphics) {
super.paintComponent(g)
val g2 = g as? Graphics2D
if (g2 != null) {
// 根据需要使用g2...
}
}
英文:
In Kotlin casting is performed using the as keyword, like:
val g2 = g as Graphics2D
You may also use a safe cast with as?, that returns null if the casting is not possible, instead of throwing an exception:
override fun paintComponent(g: Graphics) {
super.paintComponent(g)
val g2 = g as? Graphics2D
if (g2 != null) {
// Use g2 as needed...
}
}
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