【发布时间】：2014-01-26 03:48:04
【问题描述】：
为什么 java 会把一个原本是 10 的数字变成像 9.999999999999998 这样的数字？ 这是我的代码。此外，任何关于良好做法的建议将不胜感激。例如，我可以做什么来代替所有 if 语句。我的代码的目的是输入一些东西的成本和支付了多少。输出将是差额以及由此产生的必须退回的美元和硬币。这是我遇到困难的代码。
package another;
import javax.swing.JOptionPane;
/**
*
* @author Will
*/
public class Another {
public static void tryAgain() {
JOptionPane.showMessageDialog(null, "Enter a valid amount and try again");
System.exit(0);
}
/**
* @param args the command line arguments
*/
public static void main(String[] args) {
String purchase = JOptionPane.showInputDialog("Please enter a the purchase amount");
if (purchase == null) {
System.exit(0);
}
if (purchase.isEmpty()) {
tryAgain();
}
for (int i = 0; i < purchase.length(); i = i + 1) {
if (!Character.isDigit(purchase.charAt(i))
&& !purchase.contains(".")) {
tryAgain();
}
}
String given = JOptionPane.showInputDialog("Please enter the given amount");
if (given == null) {
System.exit(0);
}
if (given.isEmpty()) {
tryAgain();
}
for (int i = 0; i < given.length(); i = i + 1) {
if (!Character.isDigit(given.charAt(i))
&& !given.contains(".")) {
tryAgain();
}
}
Double a = Double.parseDouble(purchase);
Double b = Double.parseDouble(given);
Double c = b - a;
if (c < 0) {
JOptionPane.showMessageDialog(null, "Give the cashier more money!");
System.exit(0);
}
System.out.println( "Change: $" + c);
if (c > 100) {
double hundredsPlusExtra = c / 100;
double hundredsWithout = Math.floor(hundredsPlusExtra); //this line rounds down
c = c - hundredsWithout * 100;
if (hundredsWithout == 1) {
System.out.println(hundredsWithout + " One-Hundred Dollar Bill");
} else {
System.out.println(hundredsWithout + " Hundred Dollar Bills");
}
}
if (c > 50) {
double fiftiesPlusExtra = c / 50;
double fiftiesWithout = Math.floor(fiftiesPlusExtra); //this line rounds down
c = c - fiftiesWithout * 50;
if (fiftiesWithout == 1) {
System.out.println(fiftiesWithout + " Fifty Dollar Bill");
} else {
System.out.println(fiftiesWithout + " Fifty Dollar Bills");
}
}
if (c > 20) {
double twentiesPlusExtra = c / 20;
double twentiesWithout = Math.floor(twentiesPlusExtra); //this line rounds down
c = c - twentiesWithout * 20;
if (twentiesWithout == 1) {
System.out.println(twentiesWithout + " Twenty Dollar Bill");
} else {
System.out.println(twentiesWithout + " Twenty Dollar Bills");
}
}
if (c > 10) {
double tensPlusExtra = c / 10;
double tensWithout = Math.floor(tensPlusExtra); //this line rounds down
c = c - tensWithout * 10;
if (tensWithout == 1) {
System.out.println(tensWithout + " Ten Dollar Bill");
} else {
System.out.println(tensWithout + " Ten Dollar Bills");
}
}
if (c > 5) {
double fivesPlusExtra = c / 5;
double fivesWithout = Math.floor(fivesPlusExtra); //this line rounds down
c = c - fivesWithout * 5;
if (fivesWithout == 1) {
System.out.println(fivesWithout + " Five Dollar Bill");
} else {
System.out.println(fivesWithout + " Five Dollar Bills");
}
}
if (c > 1) {
double onesPlusExtra = c / 1;
double onesWithout = Math.floor(onesPlusExtra); //this line rounds down
c = c - onesWithout * 1;
if (onesWithout == 1) {
System.out.println(onesWithout + " One Dollar Bill");
} else {
System.out.println(onesWithout + " One Dollar Bills");
}
}
if (c > .25) {
double quartersPlusExtra = c / .25;
double quartersWithout = Math.floor(quartersPlusExtra); //this line rounds down
c = c - quartersWithout * .25;
if (quartersWithout == 1) {
System.out.println(quartersWithout + " Quarter");
} else {
System.out.println(quartersWithout + " Quarters");
}
}
}
}
【问题讨论】：
-
如何用二进制表示十进制数？
-
我在您的代码中看到的唯一整数是
for循环索引和整数文字。 -
对于投反对票的人，请在投反对票之前尝试搜索有关此主题的答案。 （不幸的是）根据问题中的关键字找到这个问题的相关答案并不容易。
-
我同意@AndrewThompson 的观点。每当我在关闭之前找到一个问题时，我都会将这些问题标记为重复，但我不会投反对票。对于那些已经意识到浮点舍入误差是一种普遍现象的人来说，与前面问题的关系是显而易见的。对于不了解舍入误差的人来说，它们看起来像是独特而奇怪的情况。