如何重写 compareTo() 方法，以便它返回类 obj 和 THIS 类 obj 的比较

Question

所以这是我需要遵循的方向：

重写 compareTo 方法：int compareTo( CreditCardNumber obj(，所以它(返回？(THIS CreditCardNumber 的 toString(( 的 compareTo 的结果，将参数的 (obj's( 传递给 String((。

以下是相关的代码信息：

public class CreditCardNumber implements Comparable<CreditCardNumber> {
private String issuerId = "000000";
private String accountNum = "999999999";
private int checkDigit = 9;
private StringBuilder builder;
public CreditCardNumber(String id, String accNum) {
this();
if (id == null && accNum == null && id.length() != 6 && accNum.length() != 9 && isDigit(id) == false
&& isDigit(accNum) == false) {
throw new IllegalArgumentException(
"Either parameter is null or has incorrect length or doesn't have all digits");
} else
accountNum = accNum;
issuerId = id;
setCheckDigit();
}
public CreditCardNumber() {
} // default constructor
public String getId() { // accessor
return issuerId;
}
public String getAccNum() { // accessor
return accountNum;
}
public int getCheckDigit() { // accessor
return checkDigit;
}
// A
private void setCheckDigit() { // assings checkDigit
checkDigit = 0;
int sum = checkSum();
int temp = checkDigit + sum;
if (temp % 10 != 0) {
checkDigit = (10 - (checkSum() % 10)) % 10;
}
}
// Method to check if each character in string is a digit
public boolean isDigit(String s) {
boolean isdigit = true;
for (int i = 0; i < s.length(); i++) {
if (!Character.isDigit(s.charAt(i))) {
isdigit = false;
}
}
return isdigit; // which is false
}
// B
public void changeId(String id) {
int max = 9;
int min = 0;
if (id == null || id.length() != 6 || isDigit(id) == false) {
throw new IllegalArgumentException("ID is null or length isn't correct or is not a digit");
} else {
issuerId = id;
builder = new StringBuilder();
}
for (int i = 0; i < 9 ; i++) {
int randomNum = (int) (Math.random() * (max - min + 1)) + min;
builder.append(randomNum);
accountNum = builder.toString();
}
setCheckDigit();
}
// C
private int checkSum() {
int sum = 0;
builder = new StringBuilder();
builder.append(issuerId);
builder.append(accountNum);
for (int i = 0; i < builder.length(); i++) {
// In each of the chars with an EVEN index
if (i % 2 == 0) {
int x = Character.getNumericValue(builder.charAt(i)); //// get the int value from the char
int y = x * 2; // multiply it by 2
if (y >= 10) {
int z = y % 10;
z += 1; //// if doubling it has 2 digits, add those digits
builder.setCharAt(i, Character.forDigit(z, 10)); // put above result back into the StringBuilder
// atthe same index
} else {
builder.setCharAt(i, Character.forDigit(y, 10)); // put above result back into the StringBuilder at
// the same index
}
}
}
// Add the values of each digit in the StringBuilder
for (int i = 0; i < builder.length(); i++) {
sum += Character.getNumericValue(builder.charAt(i));
}
return sum;
}
// D
public String toString() {
builder = new StringBuilder();
builder.append(issuerId).append(accountNum).append(checkDigit);
builder.insert(4, ' ');
builder.insert(9, ' ');
builder.insert(14, ' ');
return builder.toString();
}
public int compareTo(CreditCardNumber obj) { //THERES A PROBLEM HERE
}
}

我遇到的问题是我并不真正理解提示，我将不胜感激任何正确方向的帮助。

Answer 1

这里有一个可以根据您的用例进行改造的类：

class Person implements Comparable<Person> {
private final int age;
private final String name;
public Person(int age, String name) {
this.age = age;
this.name = name;
}
@Override
public String toString() {
return String.format("Age: %d, name: %s", age, name);
}
@Override
public int compareTo(Person o) {
return this.toString().compareTo(o.toString());
}
}

它使用他们的字符串表示形式比较 2 个人。String已经实现了Comparable<String>，所以你可以直接在String上调用compareTo。

现在，您可以通过按顺序打印人员来利用已实现Comparable<Person>界面的优势：

public static void main(String... args) {
List<Person> people = Arrays.asList(new Person(30, "You"), new Person(23, "Me"));
Collections.sort(people);
people.forEach(System.out::println);
}