java rookie, read java Core Technology introduction Graphics2D class is a subclass of Graphics, in which there is a code
public void paintComponent (Graphics g) {
Graphics2D g2 = (Graphics2D) g
......}
will there be no error in the downward transition here?
public class test{
public static void main(String[] args) {
Graohics g = new Graphics2D();
Graphics2D g2;
if(g instanceof Graphics2D)
g2 = (Graphics2D) g;
else
System.out.print("error");
}
}
class Graohics{
}
class Graphics2D extends Graohics{
}output:()public class test{
public static void main(String[] args) {
Graohics g = new Graphics();
Graphics2D g2 = (Graphics2D) g;
}
}java test
Exception in thread "main" java.lang.ClassCastException: Graohics cannot be cast to Graphics2D
at test.main(test.java:5)if the object you pass in is a Graphics2D, there will be no error.
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URL is not hierarchical ...