关于swing：为什么java将整数转化为更少的东西

why is java turning integers into something less

本问题已经有最佳答案，请猛点这里访问。

为什么Java把一个10的数字变成9.999999999999998？这是我的密码。此外，任何关于良好实践的建议都将受到赞赏。例如，我可以做什么来代替所有的if语句。我的代码的目的是输入一些东西的成本和支付金额。产出将是差额，以及由此产生的美元和硬币必须归还。这是我遇到困难的代码。

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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");
}
}
}
}