例：构造器，代码块在接口中统统没有，也不能创建对象

构造器的使用-----实现类

例：下图中的B类就是一个 实现类

2.接口的好处

继承只能单继承，而接口可以弥补类单继承的不足，下图中除了用student作为实现类，还可以同时使用其他类作为实现类.

接口方便业务的切换：

案例

代码：构建了如下的接口和类

packageInterfaceDemo;

importjava.util.ArrayList;

//方案一

publicclassMethod1implementsOperate{

@Override

publicvoidprintInfo(ArrayList<Student>students){

for(inti=0;i<students.size();i++){

System.out.println("姓名："+students.get(i).getName());

System.out.println("性别："+students.get(i).getSex());

System.out.println("训练成绩："+students.get(i).getScore());

}

}

@Override

publicvoidprintAver(ArrayList<Student>students){

doublesumScore=0;

for(inti=0;i<students.size();i++){

sumScore+=students.get(i).getScore();

}

System.out.println("104期学员的平均分为："+sumScore/4);

}

}

packageInterfaceDemo;

importjava.util.ArrayList;

//方案二

publicclassMethod2implementsOperate{

@Override

publicvoidprintInfo(ArrayList<Student>students){

intmaleNum=0;

intfemaleNum=0;

for(inti=0;i<students.size();i++){

if(students.get(i).getSex()=='男'){

maleNum++;

}

elsefemaleNum++;

System.out.println("姓名："+students.get(i).getName());

System.out.println("性别："+students.get(i).getSex());

System.out.println("训练成绩："+students.get(i).getScore());

}

System.out.println("该期学员男："+maleNum+"人");

System.out.println("该期学员女："+femaleNum+"人");

}

@Override

publicvoidprintAver(ArrayList<Student>students){

doublemax=students.get(0).getScore();

doublemin=students.get(0).getScore();

doublesumScore=0;

for(inti=0;i<students.size();i++){

if(students.get(i).getScore()>max)max=students.get(i).getScore();

if(students.get(i).getScore()<min)min=students.get(i).getScore();

sumScore+=students.get(i).getScore();

}

System.out.println("104期学员的平均分为："+(sumScore-max-min)/2+"分~~~");

}

}

packageInterfaceDemo;

importjava.util.ArrayList;

publicinterfaceOperate{

voidprintInfo(ArrayList<Student>students);

voidprintAver(ArrayList<Student>students);

}

packageInterfaceDemo;

publicclassStudent{

privateStringname;

privatecharsex;

privatedoublescore;

publicStudent(){

}

publicStudent(Stringname,charsex,doublescore){

this.name=name;

this.sex=sex;

this.score=score;

}

publicStringgetName(){

returnname;

}

publicvoidsetName(Stringname){

this.name=name;

}

publicchargetSex(){

returnsex;

}

publicvoidsetSex(charsex){

this.sex=sex;

}

packageInterfaceDemo;

importjava.util.ArrayList;

publicclassStuOperate{

//创建一个容器，储存学生信息

privateArrayList<Student>students=newArrayList<>();

privateOperateoperate=newMethod2();

publicvoidmanage(){

Students1=newStudent("米卡莎",'女',100);

Students2=newStudent("阿尼",'女',99);

Students3=newStudent("耶格尔",'男',99);

Students4=newStudent("阿尔敏",'男',99.5);

students.add(s1);

students.add(s2);

students.add(s3);

students.add(s4);

}

publicvoidprintAllInfo(){

operate.printInfo(students);

}

publicvoidprintAllAver(){

operate.printAver(students);

}

}

packageInterfaceDemo;

publicclasstest{

publicstaticvoidmain(String[]args){

StuOperatestuOperate=newStuOperate();

stuOperate.manage();

stuOperate.printAllInfo();

stuOperate.printAllAver();

}

}

接口好处小结：

3.接口的其他注意事项