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- What does “possible lossy conversion” mean and how do I fix it? 1 answer
“可能的有损转换”是什么意思,我该如何解决? 1个答案
I have this program that is pretty much a calculator but with a moving JLabel that is supposed to change colors every time you click the label, but i have 3 errors at the very bottom of the code that i have marked with a comment. all three are: error: incompatible types: possible lossy conversion from long to int
我有这个程序几乎是一个计算器,但是每次单击标签时都会有一个移动的JLabel,它应该会改变颜色,但是我在代码的最底部有3个错误,我用注释标记了。这三个都是:错误:不兼容的类型:从long到int的可能有损转换
public class TestCalculator {
private ResultPane resultPane;
public static void main(String[] args) {
new TestCalculator();
}
public TestCalculator() {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
resultPane = new ResultPane();
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
}
JFrame frame = new JFrame("Testing");
frame.setGlassPane(resultPane);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new BorderLayout());
frame.add(new CalculatorPane(resultPane));
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
frame.setBounds(200,200,500,400);
}
});
}
public class ResultPane extends JPanel {
private JLabel result;
private Timer timer;
private int xDelta = (Math.random() > 0.5) ? 1 : -1;
private int yDelta = (Math.random() > 0.5) ? 1 : -1;
public void setLabelForeground(Color color) {
result.setForeground(color);
}
public ResultPane() {
setOpaque(false);
setLayout(null);
result = new JLabel();
Font font = result.getFont();
font = font.deriveFont(Font.BOLD, 26f);
result.setFont(font);
add(result);
HandlerClass handler = new HandlerClass();
result.addMouseListener(handler);
result.addMouseMotionListener(handler);
timer = new Timer(40, new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
Point point = result.getLocation();
point.x += xDelta;
point.y += yDelta;
if (point.x < 0) {
point.x = 0;
xDelta *= -1;
} else if (point.x + result.getWidth() > getWidth()) {
point.x = getWidth() - result.getWidth();
xDelta *= -1;
}
if (point.y < 0) {
point.y = 0;
yDelta *= -1;
} else if (point.y + result.getHeight() > getHeight()) {
point.y = getHeight() - result.getHeight();
yDelta *= -1;
}
result.setLocation(point);
repaint();
}
});
timer.start();
}
public void setResult(Number number) {
result.setText(NumberFormat.getNumberInstance().format(number));
result.setSize(result.getPreferredSize());
setVisible(true);
}
public String getResultText() {
return result.getText();
}
}
public class CalculatorPane extends JPanel {
private final ResultPane resultPane;
private final JLabel firstNumberLabel = new JLabel("First Number:");
private final JLabel secondNumberLabel = new JLabel("Second Number:");
private final JTextField firstNumberField = new JTextField(5);
private final JTextField secondNumberField = new JTextField(5);
public double result = 0.0;
public CalculatorPane(ResultPane resultPane) {
setLayout(new GridBagLayout());
GridBagConstraints gbc = new GridBagConstraints();
gbc.gridwidth = GridBagConstraints.REMAINDER;
this.resultPane = resultPane;
JPanel fields = new JPanel();
fields.add(firstNumberLabel);
fields.add(firstNumberField);
fields.add(secondNumberLabel);
fields.add(secondNumberField);
add(fields, gbc);
JPanel buttons = new JPanel();
buttons.add(new JButton(new AddAction()));
buttons.add(new JButton(new SubtractAction()));
buttons.add(new JButton(new MultiplyAction()));
buttons.add(new JButton(new DivideAction()));
add(buttons, gbc);
}
public class AddAction extends AbstractAction {
public AddAction() {
putValue(NAME, "+");
}
@Override
public void actionPerformed(ActionEvent e) {
try {
double num1 = Double.parseDouble(firstNumberField.getText());
double num2 = Double.parseDouble(secondNumberField.getText());
double result = num1 + num2;
resultPane.setResult(result);
String resultText = resultPane.getResultText();
firstNumberField.setText(resultText);
} catch (NumberFormatException exp) {
}
}
}
public class SubtractAction extends AbstractAction {
public SubtractAction() {
putValue(NAME, "-");
}
@Override
public void actionPerformed(ActionEvent e) {
try {
double num1 = Double.parseDouble(firstNumberField.getText());
double num2 = Double.parseDouble(secondNumberField.getText());
double result = num1 - num2;
resultPane.setResult(result);
String resultText = resultPane.getResultText();
firstNumberField.setText(resultText);
} catch (NumberFormatException exp) {
}
}
}
public class MultiplyAction extends AbstractAction {
public MultiplyAction() {
putValue(NAME, "x");
}
@Override
public void actionPerformed(ActionEvent e) {
try {
double num1 = Double.parseDouble(firstNumberField.getText());
double num2 = Double.parseDouble(secondNumberField.getText());
double result = num1 * num2;
resultPane.setResult(result);
String resultText = resultPane.getResultText();
firstNumberField.setText(resultText);
} catch (NumberFormatException exp) {
}
}
}
public class DivideAction extends AbstractAction {
public DivideAction() {
putValue(NAME, "/");
}
@Override
public void actionPerformed(ActionEvent e) {
try {
double num1 = Double.parseDouble(firstNumberField.getText());
double num2 = Double.parseDouble(secondNumberField.getText());
double result = num1 / num2;
resultPane.setResult(result);
String resultText = resultPane.getResultText();
firstNumberField.setText(resultText);
} catch (NumberFormatException exp) {
}
}
}
}
private class HandlerClass implements MouseListener, MouseMotionListener {
public void mouseClicked(MouseEvent event) {
int r = Math.round(Math.random() * 255);//error here
int g = Math.round(Math.random() * 255);//here
int b = Math.round(Math.random() * 255);//and here
Color col = new Color(r, g, b);
resultPane.setLabelForeground(col);
}
public void mouseReleased(MouseEvent event) {
}
public void mousePressed(MouseEvent event) {
}
public void mouseExited(MouseEvent event) {
}
public void mouseEntered(MouseEvent event) {
}
public void mouseMoved(MouseEvent event) {
}
public void mouseDragged(MouseEvent event){
}
}
}
3 个解决方案
#1
6
That's because a long is 64 bits and an int is 32 bits, not to mention you're going from floating-point to integer. To go from long to int, you're going to have to discard some information, and the compiler can't/won't do that automatically. You're going to have to explicitly say so through a cast:
那是因为long是64位而int是32位,更不用说你从浮点到整数了。要从long转到int,你将不得不丢弃一些信息,编译器不能/不会自动执行。你将不得不通过一个演员明确地这样说:
int g = (int) Math.round(Math.random() * 255);
^^^^^
Alternatively, you can use java.util.Random:
或者,您可以使用java.util.Random:
Random r = new Random();
int g = r.nextInt(256);
#2
2
You are trying to have the compiler provide an implicit primitive narrowing conversion, by assigning a long (the result of Math.round) to an int. It cannot be done implicitly; do it explicitly with a cast.
您正在尝试让编译器通过将long(Math.round的结果)赋值给int来提供隐式原始缩小转换。它无法隐含地完成;用演员表明做。
int r = (int) Math.round(Math.random() * 255);
#3
0
Math.random() gives you a long, which can far exceed the range of values that an integer can represent. You then assign that value to an integer.
Math.random()给你一个long,它可以远远超过整数可以表示的值的范围。然后,将该值分配给整数。
That is what the compiler is warning you about.
这就是编译器警告你的内容。
http://docs.oracle.com/javase/7/docs/api/java/lang/Math.html
#1
6
That's because a long is 64 bits and an int is 32 bits, not to mention you're going from floating-point to integer. To go from long to int, you're going to have to discard some information, and the compiler can't/won't do that automatically. You're going to have to explicitly say so through a cast:
那是因为long是64位而int是32位,更不用说你从浮点到整数了。要从long转到int,你将不得不丢弃一些信息,编译器不能/不会自动执行。你将不得不通过一个演员明确地这样说:
int g = (int) Math.round(Math.random() * 255);
^^^^^
Alternatively, you can use java.util.Random:
或者,您可以使用java.util.Random:
Random r = new Random();
int g = r.nextInt(256);
#2
2
You are trying to have the compiler provide an implicit primitive narrowing conversion, by assigning a long (the result of Math.round) to an int. It cannot be done implicitly; do it explicitly with a cast.
您正在尝试让编译器通过将long(Math.round的结果)赋值给int来提供隐式原始缩小转换。它无法隐含地完成;用演员表明做。
int r = (int) Math.round(Math.random() * 255);
#3
0
Math.random() gives you a long, which can far exceed the range of values that an integer can represent. You then assign that value to an integer.
Math.random()给你一个long,它可以远远超过整数可以表示的值的范围。然后,将该值分配给整数。
That is what the compiler is warning you about.
这就是编译器警告你的内容。
http://docs.oracle.com/javase/7/docs/api/java/lang/Math.html