空指针异常

Question

题目  先把国家加入map中,然后打印出以"A"开头的国家
      二个问题,如何建立泛型数组,这里面说不能建立泛型数组,所以不好用for语句
代码:(没有注释,见谅)import java.util.*;
import java.lang.*;class Pairs<K,V>
{
public K key;
public V value;
public Pairs(K key,V value)
{
this.key=key;
this.value=value;
}
}
public class SearchMap
{
//private  Map<String,String> map;
public  void put(Pairs<String,String> p,Map<String,String> map)
{
//map=new LinkedHashMap<String,String>();
map.put(p.key,p.value);
}
public boolean judge(Pairs<String,String> p,Map<String,String> map)
{
put(p,map);
//map=new LinkedHashMap<String,String>();
StringBuffer sb=new StringBuffer((String)map.get(p.value));
if(sb.charAt(0)=='A')
{
return true;
}else
{
return false;
}
}
public static void main(String[] args)
{
SearchMap sm=new SearchMap();
Map<String,String> map1=new LinkedHashMap<String,String>();
Pairs<String,String> p1=new Pairs<String,String>("zhongguo","China");
Pairs<String,String> p2=new Pairs<String,String>("meiguo","American");
Pairs<String,String> p3=new Pairs<String,String>("zhamguo","Asha");
Pairs<String,String> p4=new Pairs<String,String>("yingguo","England");
Pairs<String,String> p5=new Pairs<String,String>("faguo","French");
Pairs<String,String> p6=new Pairs<String,String>("aodili","Australia");
    //sm.put(p1,map1);sm.put(p2,map1);sm.put(p3,map1);sm.put(p4,map1);sm.put(p5,map1);sm.put(p6,map1);
    if(sm.judge(p1,map1))
    {
     System.out.println(p1.value);
    }else if(sm.judge(p2,map1))
    {
     System.out.println(p2.value);
    }else if(sm.judge(p2,map1))
    {
     System.out.println(p1.value);
    }else if(sm.judge(p3,map1))
    {
     System.out.println(p3.value);
    }else if(sm.judge(p4,map1))
    {
     System.out.println(p4.value);
    }else if(sm.judge(p5,map1))
    {
     System.out.println(p5.value);
    }else if(sm.judge(p6,map1))
    {
     System.out.println(p6.value);
    }
}
}

Answer 1

StringBuffer sb=new StringBuffer((String)map.get(p.value)); 中map是从主方法那边传过来的,本来就是空值,是你的public  void put(Pairs <String,String> p,Map <String,String> map) 写错了,应该返回一个Map<String,String>类型

Answer 2

import java.util.*; 
import java.lang.*; class Pairs <K,V> 
{ 
public K key; 
public V value; 
public Pairs(K key,V value) 
{ 
this.key=key; 
this.value=value; 
} 
} 
public class SearchMap 
{ 
//private  Map <String,String> map; 
public  void put(Pairs <String,String> p,Map <String,String> map) 
{ 
//map=new LinkedHashMap <String,String>(); 
map.put(p.key,p.value); 
} 
public boolean judge(Pairs <String,String> p,Map <String,String> map) 
{ 
put(p,map); 
//map=new LinkedHashMap <String,String>(); 
StringBuffer sb=new StringBuffer((String)map.get(p.key)); 
if(sb.charAt(0)=='A') 
{ 
return true; 
}else 
{ 
return false; 
} 
} 
public static void main(String[] args) 
{ 
SearchMap sm=new SearchMap(); 
Map <String,String> map1=new LinkedHashMap <String,String>(); 
Pairs <String,String> p1=new Pairs <String,String>("zhongguo","China"); 
Pairs <String,String> p2=new Pairs <String,String>("meiguo","American"); 
Pairs <String,String> p3=new Pairs <String,String>("zhamguo","Asha"); 
Pairs <String,String> p4=new Pairs <String,String>("yingguo","England"); 
Pairs <String,String> p5=new Pairs <String,String>("faguo","French"); 
Pairs <String,String> p6=new Pairs <String,String>("aodili","Australia"); 
    //sm.put(p1,map1);sm.put(p2,map1);sm.put(p3,map1);sm.put(p4,map1);sm.put(p5,map1);sm.put(p6,map1); 
    if(sm.judge(p1,map1)) 
    { 
    System.out.println(p1.value); 
    }else if(sm.judge(p2,map1)) 
    { 
    System.out.println(p2.value); 
    }else if(sm.judge(p2,map1)) 
    { 
    System.out.println(p1.value); 
    }else if(sm.judge(p3,map1)) 
    { 
    System.out.println(p3.value); 
    }else if(sm.judge(p4,map1)) 
    { 
    System.out.println(p4.value); 
    }else if(sm.judge(p5,map1)) 
    { 
    System.out.println(p5.value); 
    }else if(sm.judge(p6,map1)) 
    { 
    System.out.println(p6.value); 
    } 
} 
}

Answer 3

你的对了 我也是这么改的 粗心不得啊
   呵呵
  还有一个问题是不能创建泛型数组吗??
  比如Pairs<String,String>[]  p={new Pairs<String,String>("zhongguo","China"),new Pairs<String,String>("meiguo","American"),
      new Pairs<String,String>("zhamguo","Asha"),new Pairs<String,String>("yingguo","England"),
                new Pairs<String,String>("faguo","French"),new Pairs<String,String>("aodili","Australia")};

Answer 4

报错是can't create a cast array

Answer 5

报错是can't create a cast array
   帮我解决这个了就给你分啊
  呵呵呵(只要你想想就给你)