StackOverflow社区。我正在尝试创建一个命令行应用程序来操作X和Y坐标。令我感到困惑的是，当它在案例B下询问X或Y时，它认为当我没有输入任何东西时我输入的是X或Y以外的东西。什么可以使这种情况发生？
public class OrderedPairTest {
public static void main(String[] args) {
OrderedPair op1 = new OrderedPair();
OrderedPair op2 = new OrderedPair();
OrderedPair op3 = new OrderedPair();
EasyReader console = new EasyReader();
System.out.println("Ordered Pairs 1, 2, and 3 are set to (0,0).\nWhat would you like to do?");
System.out.println("Type A to display values, B for setting values, C for moving values,\nD for string conversion, E for printing, and F for other calculations.");
char one = console.readChar();
switch(one){
case 'A':
System.out.print("Type the ordered pair's number: ");
int onea = console.readInt();
switch(onea){
case 1:
op1.getX();
op1.getY();
break;
case 2:
op2.getX();
op2.getY();
break;
case 3:
op3.getX();
op3.getY();
break;
default:
System.out.println("Invalid pair number. Returning to main menu.");
main(null);
}
main(null);
case 'B':
System.out.print("Type the ordered pair's number: ");
int oneb = console.readInt();
switch(oneb){
case 1:
System.out.print("\nX or Y?");
char twoa = console.readChar();
switch(twoa){
case 'X':
System.out.print("\nValue? ");
int valx1 = console.readInt();
op1.setX(valx1);
break;
case 'Y':
System.out.print("\nValue? ");
int valy1 = console.readInt();
op1.setY(valy1);
break;
default:
System.out.println("\nInvalid axis. Returning to the main menu.");
main(null);
}
break;
case 2:
System.out.println("X or Y?");
char twob = console.readChar();
switch(twob){
case 'X':
System.out.println("Value?");
int valx2 = console.readInt();
op1.setX(valx2);
break;
case 'Y':
System.out.println("Value?");
int valy2 = console.readInt();
op1.setY(valy2);
break;
default:
System.out.println("Invalid axis. Returning to the main menu.");
main(null);
}
break;
case 3:
System.out.println("X or Y?");
char twoc = console.readChar();
switch(twoc){
case 'X':
System.out.println("Value?");
int valx3 = console.readInt();
op1.setX(valx3);
break;
case 'Y':
System.out.println("Value?");
int valy3 = console.readInt();
op1.setY(valy3);
break;
default:
System.out.println("Invalid axis. Returning to the main menu.");
main(null);
}
break;
default:
System.out.println("Invalid pair number. Returning to main menu.");
main(null);
}
main(null);
case 'C':
System.out.print("Type the ordered pair's number: ");
int onec = console.readInt();
switch(onec){
case 1:
System.out.println("X, Y or B (Both)?");
char twoa = console.readChar();
switch(twoa){
case 'X':
System.out.println("Value?");
int valx1 = console.readInt();
op1.moveX(valx1);
break;
case 'Y':
System.out.println("Value?");
int valy1 = console.readInt();
op1.moveY(valy1);
break;
case 'B':
System.out.println("Value of X?");
int valx4 = console.readInt();
System.out.println("Value of Y?");
int valy4 = console.readInt();
op1.moveXY(valx4,valy4);
break;
default:
System.out.println("Invalid axis. Returning to the main menu.");
main(null);
}
break;
case 2:
System.out.println("X or Y?");
char twob = console.readChar();
switch(twob){
case 'X':
System.out.println("Value?");
int valx5 = console.readInt();
op1.moveX(valx5);
break;
case 'Y':
System.out.println("Value?");
int valy5 = console.readInt();
op1.moveY(valy5);
break;
case 'B':
System.out.println("Value of X?");
int valx2 = console.readInt();
System.out.println("Value of Y?");
int valy2 = console.readInt();
op1.moveXY(valx2,valy2);
break;
default:
System.out.println("Invalid axis. Returning to the main menu.");
main(null);
}
break;
case 3:
System.out.println("X or Y?");
char twoc = console.readChar();
switch(twoc){
case 'X':
System.out.println("Value?");
int valx3 = console.readInt();
op1.moveX(valx3);
break;
case 'Y':
System.out.println("Value?");
int valy3 = console.readInt();
op1.moveY(valy3);
break;
case 'B':
System.out.println("Value of X?");
int valx6 = console.readInt();
System.out.println("Value of Y?");
int valy6 = console.readInt();
op1.moveXY(valx6,valy6);
break;
default:
System.out.println("Invalid axis. Returning to the main menu.");
main(null);
}
break;
default:
System.out.println("Invalid pair number. Returning to main menu.");
main(null);
}
main(null);
case 'D':
System.out.print("Type the ordered pair's number: ");
int oned = console.readInt();
switch(oned){
case 1:
op1.toString();
break;
case 2:
op2.toString();
break;
case 3:
op3.toString();
break;
default:
System.out.println("Invalid pair number. Returning to main menu.");
main(null);
}
main(null);
case 'E':
System.out.print("Type the ordered pair's number: ");
int onee = console.readInt();
switch(onee){
case 1:
op1.printOP();
break;
case 2:
op2.printOP();
break;
case 3:
op3.printOP();
break;
default:
System.out.println("Invalid pair number. Returning to main menu.");
main(null);
}
main(null);
case 'F':
System.out.print("Type the first ordered pair's number: ");
int onef = console.readInt();
System.out.print("\nType the second ordered pair's number: ");
int oneg = console.readInt();
switch(onef){
case 1:
switch(oneg){
case 2:
op1.distance(op2);
op1.midpoint(op2);
break;
case 3:
op1.distance(op3);
op1.midpoint(op3);
break;
default:
System.out.println("Invalid pair number. Returning to main menu.");
main(null);
}
case 2:
switch(oneg){
case 1:
op2.distance(op1);
op2.midpoint(op1);
break;
case 3:
op2.distance(op3);
op2.midpoint(op3);
break;
default:
System.out.println("Invalid pair number. Returning to main menu.");
main(null);
}
case 3:
switch(oneg){
case 1:
op3.distance(op1);
op3.midpoint(op1);
break;
case 2:
op3.distance(op2);
op3.midpoint(op2);
break;
default:
System.out.println("Invalid pair number. Returning to main menu.");
main(null);
}
default:
System.out.println("Invalid pair number. Returning to main menu.");
main(null);
}
main(null);
default:
System.out.println("Invalid option. Returning to main menu.");
main(null);
}
}
}
这是我的EasyReader类，用于调试目的。它不是我的，但它简化了读取字符串，整数和字符：
public class EasyReader
{
protected String myFileName;
protected BufferedReader myInFile;
protected int myErrorFlags = 0;
protected static final int OPENERROR = 0x0001;
protected static final int CLOSEERROR = 0x0002;
protected static final int READERROR = 0x0004;
protected static final int EOF = 0x0100;
/**
* Constructor. Prepares console (System.in) for reading
*/
public EasyReader()
{
myFileName = null;
myErrorFlags = 0;
myInFile = new BufferedReader(
new InputStreamReader(System.in), 128);
}
/**
* Constructor. opens a file for reading
* @param fileName the name or pathname of the file
*/
public EasyReader(String fileName)
{
myFileName = fileName;
myErrorFlags = 0;
try
{
myInFile = new BufferedReader(new FileReader(fileName), 1024);
}
catch (FileNotFoundException e)
{
myErrorFlags |= OPENERROR;
myFileName = null;
}
}
/**
* Closes the file
*/
public void close()
{
if (myFileName == null)
return;
try
{
myInFile.close();
}
catch (IOException e)
{
System.err.println("Error closing " + myFileName + "\n");
myErrorFlags |= CLOSEERROR;
}
}
/**
* Checks the status of the file
* @return true if en error occurred opening or reading the file,
* false otherwise
*/
public boolean bad()
{
return myErrorFlags != 0;
}
/**
* Checks the EOF status of the file
* @return true if EOF was encountered in the previous read
* operation, false otherwise
*/
public boolean eof()
{
return (myErrorFlags & EOF) != 0;
}
private boolean ready() throws IOException
{
return myFileName == null || myInFile.ready();
}
/**
* Reads the next character from a file (any character including
* a space or a newline character).
* @return character read or <code>null</code> character
* (Unicode 0) if trying to read beyond the EOF
*/
public char readChar()
{
char ch = '\u0000';
try
{
if (ready())
{
ch = (char)myInFile.read();
}
}
catch (IOException e)
{
if (myFileName != null)
System.err.println("Error reading " + myFileName + "\n");
myErrorFlags |= READERROR;
}
if (ch == '\u0000')
myErrorFlags |= EOF;
return ch;
}
/**
* Reads from the current position in the file up to and including
* the next newline character. The newline character is thrown away
* @return the read string (excluding the newline character) or
* null if trying to read beyond the EOF
*/
public String readLine()
{
String s = null;
try
{
s = myInFile.readLine();
}
catch (IOException e)
{
if (myFileName != null)
System.err.println("Error reading " + myFileName + "\n");
myErrorFlags |= READERROR;
}
if (s == null)
myErrorFlags |= EOF;
return s;
}
/**
* Skips whitespace and reads the next word (a string of consecutive
* non-whitespace characters (up to but excluding the next space,
* newline, etc.)
* @return the read string or null if trying to read beyond the EOF
*/
public String readWord()
{
StringBuffer buffer = new StringBuffer(128);
char ch = ' ';
int count = 0;
String s = null;
try
{
while (ready() && Character.isWhitespace(ch))
ch = (char)myInFile.read();
while (ready() && !Character.isWhitespace(ch))
{
count++;
buffer.append(ch);
myInFile.mark(1);
ch = (char)myInFile.read();
};
if (count > 0)
{
myInFile.reset();
s = buffer.toString();
}
else
{
myErrorFlags |= EOF;
}
}
catch (IOException e)
{
if (myFileName != null)
System.err.println("Error reading " + myFileName + "\n");
myErrorFlags |= READERROR;
}
return s;
}
/**
* Reads the next integer (without validating its format)
* @return the integer read or 0 if trying to read beyond the EOF
*/
public int readInt()
{
String s = readWord();
if (s != null)
return Integer.parseInt(s);
else
return 0;
}
/**
* Reads the next double (without validating its format)
* @return the number read or 0 if trying to read beyond the EOF
*/
public double readDouble()
{
String s = readWord();
if (s != null)
return Double.parseDouble(s);
// in Java 1, use: return Double.valueOf(s).doubleValue();
else
return 0.0;
}
}
最后，这是我的OrderedPair类：
public class OrderedPair {
int a,b;
String q = "";
public int getX() {
System.out.println("X is "+a);
return a;
}
public int getY() {
System.out.println("Y is "+b);
return b;
}
public void setX(int x) {
a = x;
System.out.println("X has been set to "+a);
if (b != 0) setQ();
else;
}
public void setY(int y) {
b = y;
System.out.println("Y has been set to "+b);
if (a != 0) setQ();
else;
}
public String toString() {
String msg = ("("+a+","+b+") Q"+q);
System.out.println("Values have been converted into string.");
return msg;
}
public int moveX(int amt) {
a+=amt;
System.out.println("X has been moved "+amt+" units.");
if ((b != 0) && (a != 0)) setQ();
else;
return a;
}
public int moveY(int amt) {
b+=amt;
System.out.println("Y has been moved "+amt+" units.");
if ((b != 0) && (a != 0)) setQ();
else;
return b;
}
public void moveXY(int amt1, int amt2){
a+=amt1;
b+=amt2;
System.out.println("X has been moved "+amt1+" units.");
System.out.println("Y has been moved "+amt2+" units.");
if ((b != 0) && (a != 0)) setQ();
else;
}
public void distance(OrderedPair other) {
double d = Math.sqrt(Math.pow(other.b-this.b,2)+Math.pow(other.a-this.a,2));
System.out.println("The distance between the two points is: "+d);
}
public void midpoint(OrderedPair other) {
int x3 = (this.a+other.a)/2;
int y3 = (this.b+other.b)/2;
System.out.println("The midpoint is at: ("+x3+","+y3+")");
}
public void printOP() {
if (q!= "") System.out.println("("+a+","+b+") Q"+q);
else System.out.println("Q has not been set.");
}
private void setQ() {
if ((a!=0)&&(b!=0)){
if (a > 0){
if (b > 0) q = "I";
else q = "IV";
}
else {
if (b > 0) q = "II";
else q = "III";
}
System.out.println("The quadrant has been set.");
}
else System.out.println("X and/or Y are zero, please assign the variables a nonzero value.");
}
}
答案 0 :(得分：1)
在读入char之前尝试添加console.skipLine();。正如评论员指出的那样，当你使用readChar时，你可能正在读取endOfLine字符（但是如果你发布完整的，可编译的代码，包括你的类定义，它会更容易调试。）
答案 1 :(得分：0)
正在读取空白区域。如果你插入
console.readLine();
这会读取不需要的内容，然后您可以根据需要使用代码。对案例1修改代码如下（类似于案例2和3），它可以工作：
case 1:
System.out.print("\nX or Y?");
console.readLine();
char twoa = console.readChar();
我通过插入行
找到了这个System.out.println("twoa: "+twoa);
代码中的正确位置（见下文）
case 1:
System.out.print("\nX or Y?");
char twoa = console.readChar();
System.out.println("twoa: "+twoa);
运行程序的结果如下：
Ordered Pairs 1, 2, and 3 are set to (0,0).
What would you like to do?
Type A to display values, B for setting values, C for moving values,
D for string conversion, E for printing, and F for other calculations.
B
Type the ordered pair's number: 1
X or Y?
twoa:
Invalid axis. Returning to the main menu.
Ordered Pairs 1, 2, and 3 are set to (0,0).
What would you like to do?
Type A to display values, B for setting values, C for moving values,
D for string conversion, E for printing, and F for other calculations.
注意这一行
twoa:
显示console.readChar（）读取空格，然后将其分配给行中的字符'twoa'
char twoa = console.readChar();
如果你想了解程序正在做什么，插入这样的打印语句会有所帮助。