Java零基础教程-面向对象封装性

控制对年龄的修改，年龄只能为大于等于 0 并且小于等于 120 的值

public class OOTest03 {

public static void main(String[] args) {

//创建一个对象

Student zhangsan = new Student();

/*

zhangsan.id = 1001;

zhangsan.name = "张三";

zhangsan.sex = true;

zhangsan.address = "北京";

zhangsan.age = 20;

*/

zhangsan.setId(1001);

zhangsan.setName("张三");

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 {

//学号

int id;

//姓名

String name;

//性别 

boolean sex;

//地址

String address;

//年龄

int age;

//设置学号

public void setId(int studentId) {

id = studentId; 

}

//读取学号

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

age = studentAge;

}

}

public int getAge() {

return age;

}

}

从上面的示例，采用方法可以控制赋值的过程，加入了对年龄的检查，避免了直接操纵 student

属性，这就是封装， 封装其实就是封装属性，让外界知道这个类的状态越少越好。以上仍然

不完善，采用属性仍然可以赋值，如果屏蔽掉属性的赋值，只采用方法赋值，如下：

public class OOTest04 {

public static void main(String[] args) {

//创建一个对象

Student zhangsan = new Student();

zhangsan.id = 1001;

zhangsan.name = "张三";

zhangsan.sex = true;

zhangsan.address = "北京";

zhangsan.age = 20;

/*

zhangsan.setId(1001);

zhangsan.setName("张三");

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 {

//学号

private int id;

//姓名

private String name;

//性别

private boolean sex;

//地址

private String address;

//年龄

private int age;

//设置学号

public void setId(int studentId) {

id = studentId; 

}

//读取学号

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 来声明成员变量，那么此时的成员变量只属于 Student，外界无法访问，这

样就封装了我们的属性，那么属性只能通过方法访问，通过方法我们就可以控制对内部状态

的读取权利。

封装属性，暴露方法