java - Java 中 int 与其旧值的比较

Question

我正在编写一些代码，我需要确定最后一个循环中整数发生了多少变化。

我的代码:

import gnu.io.CommPort;
import gnu.io.CommPortIdentifier;
import gnu.io.SerialPort;
import com.leapmotion.leap.*;

import java.io.IOException;

import com.leapmotion.leap.Gesture.State;
import java.io.OutputStream;

import com.leapmotion.leap.Controller;
import com.leapmotion.leap.Frame;
import com.leapmotion.leap.Listener;
import java.lang.Math;

class SampleListenerMain extends Listener {

public void onInit(Controller controller) {
System.out.println("Initialized");
}

public void onConnect(Controller controller) {
System.out.println("Connected");
controller.enableGesture(Gesture.Type.TYPE_SWIPE);
controller.enableGesture(Gesture.Type.TYPE_CIRCLE);
controller.enableGesture(Gesture.Type.TYPE_SCREEN_TAP);
controller.enableGesture(Gesture.Type.TYPE_KEY_TAP);


}

public void onDisconnect(Controller controller) {
System.out.println("Disconnected");
}

public void onExit(Controller controller) {
System.out.println("Exited");
}
public void onFrame(Controller controller) {


Frame frame = controller.frame();

Hand hand = frame.hands().rightmost();
float positionx = hand.palmPosition().getX();
System.out.println("X: " + positionx);

float positiony = hand.palmPosition().getY();
System.out.println("Y:" + positiony);

float positionz = hand.palmPosition().getZ();
System.out.println("Z: " + positionz);

System.out.println("Hands: " + frame.hands().count());

int in_min = -117;
int in_max = 117;
int out_min = 900;
int out_max = 1900;
int in_min2 = -73;
int in_max2 = 73;

int positionmapx = (int) ((positionx - in_min) * (out_max - out_min) /     (in_max - in_min)) + out_min;
int positionmapy = (int) ((positiony - in_min) * (out_max - out_min) / (in_max - in_min)) + out_min;
int positionmapz = (int) ((positionz - in_min) * (out_max - out_min) / (in_max2 - in_min)) + out_min;


if (frame.hands().count() == 0) {
    LeapDrone.writeToArduino("0");
}


int posmapxold = 0;
int posmapyold = 0;
int posmapzold = 0;


String data = Integer.toString(positionmapy)+":"+     Integer.toString(positionmapx)+":"+Integer.toString(positionmapz);

System.out.println("data: " + data);


System.out.println("Old X: " + posmapxold);

System.out.println("Difference X: " + Math.abs(positionmapy - posmapyold));

if (Math.abs(positionmapx - posmapxold) >= 25) {


    LeapDrone.writeToArduino(data);

    try {
        Thread.sleep(50);
    } catch (InterruptedException e) {

        e.printStackTrace();
    }

}

if (Math.abs(positionmapy - posmapyold) >= 25) {


    LeapDrone.writeToArduino(data);

    try {
        Thread.sleep(50);
    } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}

if (Math.abs(positionmapz - posmapzold) >= 25) {


    LeapDrone.writeToArduino(data);

    try {
        Thread.sleep(50);
    } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}

posmapxold = positionmapx;
posmapyold = positionmapy;
posmapzold = positionmapz;

System.out.println("New-Old X: " + posmapxold);

try {
    Thread.sleep(100);
} catch (InterruptedException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
}

GestureList gestures = frame.gestures();
for (int i = 0; i < gestures.count(); i++) {
    Gesture gesture = gestures.get(i);



}
}
}

   class LeapDrone {
static OutputStream out = null;

public static void main(String[] args) {
//Connect to Arduino BT

try
{
(new LeapDrone()).connect("/dev/cu.usbmodem1421");
}
   catch ( Exception e )
{
    e.printStackTrace();
System.exit(0);
}

// Create a sample listener and controller
SampleListenerMain listener = new SampleListenerMain();
Controller controller = new Controller();

// Have the sample listener receive events from the controller
controller.addListener(listener);
// Keep this process running until Enter is pressed
System.out.println("Press Enter to quit...");
try {
System.in.read();
} catch (IOException e) {
e.printStackTrace();
}

// Remove the sample listener when done
controller.removeListener(listener);
}

void connect ( String portName ) throws Exception {

CommPortIdentifier portIdentifier =     CommPortIdentifier.getPortIdentifier(portName);
if ( portIdentifier.isCurrentlyOwned() )
{
System.out.println("Error: Port is currently in use");
}
else
{
CommPort commPort = portIdentifier.open(this.getClass().getName(),2000);

if ( commPort instanceof SerialPort )
{
SerialPort serialPort = (SerialPort) commPort;
serialPort.setSerialPortParams(9600,SerialPort.DATABITS_8,SerialPort.STOPBITS_1,
SerialPort.PARITY_NONE);
out = serialPort.getOutputStream();
}
else
{
System.out.println("Error: Only serial ports are handled by this example.");
}
}
}

public static void writeToArduino(String data)
{
String tmpStr = data;
byte bytes[] = tmpStr.getBytes();
try {
out.write(bytes);
} catch (IOException e) { }
}
}

例如，我有整数 i。我想运行一个循环，看看我改变了多少(在我的例子中，我被分配给一个改变每个循环的x坐标)。一旦在该循环中设置了 i，我就将整数 j 设置为等于 i。然后我需要比较 i 和 j。

问题是我必须将 j 定义为等于某个值才能初始化它。这意味着，例如，如果我通过将 j 设置为 0 来初始化它，那么每次我的代码循环时它都会重置为 0，这意味着我无法将 i 与其旧值(应该是 j)进行比较。 ......

我尝试使用“for”语句，但出现错误，因为稍后在我的代码中，当我比较 i 和 j 时，它说 j 尚未初始化......我想是因为 for 循环中的代码没有初始化不一定在程序开始时运行？

抱歉，这个问题令人困惑......我很难解释!

非常感谢任何帮助!!!

Answer 1

如果没有一些示例代码可供查看，很难提供答案，但您应该能够将先前的值初始化为循环外的初始值。

例如:

// Initialize our previous value to be the current value right off the bat
previousValue = currentValue;

for (int index = 0; index < whatever; index++) {

   // Do something that changes the value
   currentValue = someNewValue();

   // Calculate our delta
   delta = currentValue - previousValue;

   // Set our previous value to the new current value
   previousValue = currentValue;

}

如果由于某种原因 currentValue 只能在循环中计算，那么您可以使用对象类型 Integer 而不是原始 int< 为第一次迭代添加特殊情况 为前一个值键入一个 null 值以表示其第一次迭代，或者使用一个 boolean 标志，如下所示:

boolean firstIteration = true;

for (int index = 0; index < whatever; index++) {

   currentValue = someNewValue();

   if (firstIteration) {

      // Our first iteration has a zero delta
      delta = 0;
      firstIteration = false;

   } else {

      // Subsequent iterations compare the previous value
      delta = currentValue - previousValue;

   }

   previousValue = currentValue;

}