import?java.util.HashSet;
import?java.util.Set;
/**
?*?學(xué)生類
?*?@author?Administrator
?*
?*/
public?class?StudentCls?{
public?String?name;
public?String?id;
// public?Set<CourseCls>?couSet;
public?StudentCls(String?name,String?id){
this.name=name;
this.id=id;
// this.couSet=new?HashSet<CourseCls>();
}
}
import?java.util.*;
public?class?MapTest?{
public?Map<String,?StudentCls>?students;
public?void?putTest(){
Scanner?sca=new?Scanner(System.in);
int?i=0;
while(i<3){
System.out.println("請(qǐng)輸入學(xué)生ID");
String?ID=sca.next();
StudentCls?stu=students.get(ID);
if(stu==null){
System.out.println("請(qǐng)輸入學(xué)生姓名：");
String?name=sca.nextLine();
StudentCls?newstu=new?StudentCls(name,?ID);
students.put(ID,?newstu);
System.out.println("成功添加學(xué)生"+students.get(ID).name);
i++;
}
else{
System.out.println("已有該學(xué)生！");
}
}
}
public?void?ketSet(){
Set<String>?keyset=students.keySet();
System.out.println("總共有"+keyset.size()+"個(gè)學(xué)生");
for(String?id:keyset){
StudentCls?stu=students.get(id);
if(stu!=null){
System.out.println("學(xué)生："+stu.name);
}
}
}
public?static?void?main(String[]?args)?{
MapTest?mt=new?MapTest();
mt.putTest();
mt.ketSet();
}
}
MapTest中putTest()方法這句/*StudentCls stu=students.get(ID);*/報(bào)空指針異常，求解?。?！
_坐看云起時(shí)
2016-04-12 21:59:35
