Question

所以这是我需要遵循的方向：

覆盖compareTo方法：int compareTo（CreditCardNumber obj），所以它（返回？）对于THIS CreditCardNumber＆to; string（）传递参数＆（39）的compareTo的结果（obj＆＃39; s）toString（）。

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

}
}

我遇到的问题是我不太了解提示，我会感谢任何正确方向的帮助。

Answer 1

这是一个可以根据您的用例进行改造的课程：

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());
    }
}

它使用字符串表示法比较2个人。 String已实施Comparable<String>，因此您可以直接在compareTo上致电String。

您现在可以通过按顺序打印人员来实现Comparable<Person>界面：

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);
}

如何覆盖compareTo（）方法，以便返回类obj和THIS类obj的比较

1 个答案: