//通过编译,但运行时发生这个java.lang.NullPointerException错误
我的代码如下:
interface User
{
public abstract void setUser_id(String user_id);
public abstract String getUser_id();
}
abstract class AbstractUser implements User{
private String user_id;
public void setUser_id(String user_id){
this.user_id = user_id;
}
public String getUser_id(){
return user_id;
}
}
class SqlUser extends AbstractUser{
User user=null ;
public User getUser(String ID)
{
user.setUser_id(ID);
return user;
}
}
public class Test
{
public static void main(String[] args)
{
System.out.println("开始了:");
SqlUser sqlUser=new SqlUser();
User user= sqlUser.getUser("测试");
}
}
我的代码如下:
interface User
{
public abstract void setUser_id(String user_id);
public abstract String getUser_id();
}
abstract class AbstractUser implements User{
private String user_id;
public void setUser_id(String user_id){
this.user_id = user_id;
}
public String getUser_id(){
return user_id;
}
}
class SqlUser extends AbstractUser{
User user=null ;
public User getUser(String ID)
{
user.setUser_id(ID);
return user;
}
}
public class Test
{
public static void main(String[] args)
{
System.out.println("开始了:");
SqlUser sqlUser=new SqlUser();
User user= sqlUser.getUser("测试");
}
}
{
public abstract void setUser_id(String user_id); public abstract String getUser_id();
}
这就断了
public class SqlUser extends AbstractUser{
// User user=null ;
public User getUser(String ID)
{
// user.setUser_id(ID);
setUser_id(ID);
return this;
}}
public class Test {
public static void main(String[] args) {
System.out.println("开始了: ");
User sqlUser = new SqlUser().getUser("测试 ");
// User user = sqlUser.getUser("测试 ");
System.out.println(sqlUser.getUser_id());
}
}