static关键字 静态成员变量
public class Cat{
private static int sid=0;
private String name;
int id;
Cat(String name){
this.name=name;
id=sid++;
}
public void info(){
System.out.println("My name is "+name+" No."+id);
}
public static void main(String[] args) {
Cat tom=new Cat("tom");
tom.sid=100;
Cat jack=new Cat("jack");
tom.info();
jack.info();
}
}
输出：
My name is tom No.0
My name is jack No.100
使用ECLIPSE ALT+SHIFT+S自动快速生成的代码
类的继承与权限控制
class Person {
private String name;
private int age;
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;
}
}
class Student extends Person {
private String school;
public String getSchool() {
return school;
}
public void setSchool(String school) {
this.school = school;
}
}
public class test {
public static void main(String[] args) {
Student student = new Student();
student.setName("zzk");
student.setAge(23);
student.setSchool("MIT");
System.out.println(student.getName());
System.out.println(student.getAge());
System.out.println(student.getSchool());
}
}
zzk
23
MIT
重写：
class Person {
private String name;
private int age;
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 getInfo() {
return "Name: "+name+"\n"+"age:"+age;
}
}
class Student extends Person {
private String school;
public String getSchool() {
return school;
}
public void setSchool(String school) {
this.school = school;
}
public String getInfo() {
return "Name: "+getName()+"\nage"+getAge()+"\nschool:"+school;
}
}
public class test {
public static void main(String[] args) {
Student student=new Student();
Person person=new Person();
person.setName("Tom");
person.setAge(28);
student.setName("Jack");
student.setAge(23);
student.setSchool("MIT");
System.out.println(person.getInfo());
System.out.println(student.getInfo());
}
}
输出：
Name: Tom
age:28
Name: Jack
age23
school:MIT
构造函数与一般成员函数在继承中的区别
class A {
protected void print(String s) {
System.out.println(s);
}
A() {print("A()");};
public void f() {print("A:f()");};
}
class test extends A {
test() {print("B()");};
public void f() {print("B:f()");}
public static void main(String[] args) {
test b=new test();
b.f();
}
}
输出：
A()
B()
B:f()
构造方法调用
class Person {
private String name;
private String location;
Person(String name) {
this.name=name;
location="beijing";
}
Person(String name,String location) {
this.name=name;
this.location=location;
}
public String info() {
return "name: "+name+" location: "+location;
}
}
class Student extends Person {
private String school;
Student(String name,String school) {
this(name,"beijing ",school);
}
Student(String n,String l,String school) {
super(n,l);
this.school=school;
}
public String info() {
return super.info()+" school: "+school;
}
}
public class test {
public static void main(String[] ars) {
Person p1=new Person("A");
Person p2=new Person("B","shanghai");
Student s1=new Student("C","S1");
Student s2=new Student("C","shanghai","S2");
System.out.println(p1.info());
System.out.println(p2.info());
System.out.println(s1.info());
System.out.println(s2.info());
}
}
输出：
name: A location: beijing
name: B location: shanghai
name: C location: beijing school: S1
name: C location: shanghai school: S2
//构造Teacher类，继承Person类
//增加“职称”（String）属性
//具有和Student类类似的重载构造方法
//重写Person类的info()方法，增加“职称”信息
class Person {
private String name;
private String location;
Person(String name) {
this.name=name;
location="beijing";
}
Person(String name,String location) {
this.name=name;
this.location=location;
}
public String info() {
return "name: "+name+" location: "+location;
}
}
class Teacher extends Person {
private String profession;
Teacher(String name,String profession) {
this(name,"beijing",profession);
}
Teacher(String n,String l,String profession) {
super(n,l);
this.profession=profession;
}
public String info() {
return super.info()+" profession: "+profession;
}
}
class Student extends Person {
private String school;
Student(String name,String school) {
this(name,"beijing ",school);
}
Student(String n,String l,String school) {
super(n,l);
this.school=school;
}
public String info() {
return super.info()+" school: "+school;
}
}
public class test {
public static void main(String[] ars) {
Person p1=new Person("A");
Person p2=new Person("B","shanghai");
Student s1=new Student("C","S1");
Student s2=new Student("C","shanghai","S2");
Teacher t1=new Teacher("D","phd");
Teacher t2=new Teacher("D","haerbin","doc");
System.out.println(p1.info());
System.out.println(p2.info());
System.out.println(s1.info());
System.out.println(s2.info());
System.out.println(t1.info());
System.out.println(t2.info());
}
}输出：
name: A location: beijing
name: B location: shanghai
name: C location: beijing school: S1
name: C location: shanghai school: S2
name: D location: beijing profession: phd
name: D location: haerbin profession: doc
