控制對年齡的修改，年齡只能為大于等于 0 并且小于等于 120 的值

public class OOTest03 {

public static void main(String[] args) {

//創建一個對象

Student zhangsan = new Student();

/*

zhangsan.id = 1001;

zhangsan.name = "張三";

zhangsan.sex = true;

zhangsan.address = "北京";

zhangsan.age = 20;

*/

zhangsan.setId(1001);

zhangsan.setName("張三");

zhangsan.setSex(true);

zhangsan.setAddress("北京");

zhangsan.setAge(-20);

System.out.println("id=" + zhangsan.id);

System.out.println("name=" + zhangsan.name);

System.out.println("sex=" + zhangsan.sex);

System.out.println("address=" + zhangsan.address);

System.out.println("age=" + zhangsan.age);

} 

}

class Student {

//學號

int id;

//姓名

String name;

//性別 

boolean sex;

//地址

String address;

//年齡

int age;

//設置學號

public void setId(int studentId) {

id = studentId; 

}

//讀取學號

public int getId() {

return id;

}

public void setName(String studentName) {

name = studentName;

}

public String getName() {

return name;

}

public void setSex(boolean studentSex) {

sex = studentSex;

}

public boolean getSex() {

return sex;

}

public void setAddress(String studentAddress) {

address = studentAddress;

}

public String getAddress() {

return address;

}

public void setAge(int studentAge) { 

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9

if (studentAge >=0 && studentAge <=120) {

age = studentAge;

}

}

public int getAge() {

return age;

}

}

從上面的示例，采用方法可以控制賦值的過程，加入了對年齡的檢查，避免了直接操縱 student

屬性，這就是封裝， 封裝其實就是封裝屬性，讓外界知道這個類的狀態越少越好。以上仍然

不完善，采用屬性仍然可以賦值，如果屏蔽掉屬性的賦值，只采用方法賦值，如下：

public class OOTest04 {

public static void main(String[] args) {

//創建一個對象

Student zhangsan = new Student();

zhangsan.id = 1001;

zhangsan.name = "張三";

zhangsan.sex = true;

zhangsan.address = "北京";

zhangsan.age = 20;

/*

zhangsan.setId(1001);

zhangsan.setName("張三");

zhangsan.setSex(true);

zhangsan.setAddress("北京");

zhangsan.setAge(20);

*/

/*

System.out.println("id=" + zhangsan.id);

System.out.println("name=" + zhangsan.name);

System.out.println("sex=" + zhangsan.sex);

System.out.println("address=" + zhangsan.address);

System.out.println("age=" + zhangsan.age);

*/

System.out.println("id=" + zhangsan.getId());

System.out.println("name=" + zhangsan.getName());

System.out.println("sex=" + zhangsan.getSex());

System.out.println("address=" + zhangsan.getAddress()); 

System.out.println("age=" + zhangsan.getAge()); 

} 

}

class Student {

//學號

private int id;

//姓名

private String name;

//性別

private boolean sex;

//地址

private String address;

//年齡

private int age;

//設置學號

public void setId(int studentId) {

id = studentId; 

}

//讀取學號

public int getId() {

return id;

}

public void setName(String studentName) {

name = studentName;

}

public String getName() {

return name;

}

public void setSex(boolean studentSex) {

sex = studentSex;

} 

public boolean getSex() {

return sex;

}

public void setAddress(String studentAddress) {

address = studentAddress;

}

public String getAddress() {

return address;

}

public void setAge(int studentAge) {

if (studentAge >=0 && studentAge <=120) {

age = studentAge;

}

}

public int getAge() {

return age;

}

}

以上采用 private 來聲明成員變量，那么此時的成員變量只屬于 Student，外界無法訪問，這

樣就封裝了我們的屬性，那么屬性只能通過方法訪問，通過方法我們就可以控制對內部狀態

的讀取權利。

封裝屬性，暴露方法