Java是一種面向對象的編程語言，通過定義不同的類來實現不同的功能。在學生管理系統中，我們需要定義學生類和借書卡類，來記錄學生的基本信息和借書卡的狀態。

public class Student {
private String name;
private int age;
private String gender;
private String id;
private String major;
// 構造函數
public Student(String name, int age, String gender, String id, String major) {
this.name = name;
this.age = age;
this.gender = gender;
this.id = id;
this.major = major;
}
// getter 和 setter 方法
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getGender() {
return gender;
}
public void setGender(String gender) {
this.gender = gender;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getMajor() {
return major;
}
public void setMajor(String major) {
this.major = major;
}
}

上面的學生類定義了學生的基本信息，通過構造函數和getter / setter 方法來實現對學生對象的初始化和訪問。

public class BorrowCard {
private int cardId;
private String borrowDate;
private int borrowTimes;
private double fine;
// 構造函數
public BorrowCard(int cardId, String borrowDate, int borrowTimes, double fine) {
this.cardId = cardId;
this.borrowDate = borrowDate;
this.borrowTimes = borrowTimes;
this.fine = fine;
}
// getter 和 setter 方法
public int getCardId() {
return cardId;
}
public void setCardId(int cardId) {
this.cardId = cardId;
}
public String getBorrowDate() {
return borrowDate;
}
public void setBorrowDate(String borrowDate) {
this.borrowDate = borrowDate;
}
public int getBorrowTimes() {
return borrowTimes;
}
public void setBorrowTimes(int borrowTimes) {
this.borrowTimes = borrowTimes;
}
public double getFine() {
return fine;
}
public void setFine(double fine) {
this.fine = fine;
}
}

上面的借書卡類定義了借書卡的狀態信息，包括卡號、借書時間、借書次數、罰款金額。同樣通過構造函數和getter / setter 方法來實現對借書卡對象的初始化和訪問。