java.lang.NullPointerException如何修复
这是连接池的一个示例。我想我已经初始化了所有对象,但是我得到了空指针异常。我怎样才能解决这个问题java.lang.NullPointerException如何修复,java,Java,这是连接池的一个示例。我想我已经初始化了所有对象,但是我得到了空指针异常。我怎样才能解决这个问题 package hello; public class C { public static void main(String[] args) { CConnectionManager con=new CConnectionManager(); CConnection conn=new CConnection(); conn=con.GetConnection(
package hello;
public class C {
public static void main(String[] args) {
CConnectionManager con=new CConnectionManager();
CConnection conn=new CConnection();
conn=con.GetConnection();
}
public static class CConnectionManager {
private static final int MaxConSize=10;
private CConnection[] connections ;
{
connections=new CConnection[MaxConSize];
}
public CConnection GetConnection(){
for(int i=0;i<connections.length;i++){
if(1==connections[i].status){
continue;
}
else if(0==connections[i].status){
connections[i].status=1;
connections[i].pos=i;
return connections[i];
}
}
System.out.println("No connection available,Please wait");
return null;
}
public void CloseConnection (CConnection con){
if(-1==con.pos||0==con.pos){
System.out.println("No such connection");
}
else
connections[con.pos].status=0;
}
public void execute(String sql){
System.out.println(sql);
}
}
public static class CConnection {
private int status=0;
private int pos=-1;
}
}
Exception in thread "main" java.lang.NullPointerException
at hello.C$CConnection.access$0(C.java:55)
at hello.C$CConnectionManager.GetConnection(C.java:22)
at hello.C.main(C.java:8)
包你好;
公共C类{
公共静态void main(字符串[]args){
CConnectionManager con=新的CConnectionManager();
CConnection conn=新CConnection();
conn=con.GetConnection();
}
公共静态类CConnectionManager{
专用静态最终整数MaxConSize=10;
专用CConnection[]连接;
{
连接=新的CConnection[MaxConSize];
}
公共CConnection GetConnection(){
对于(int i=0;i您正在声明一个包含10个CConnection
(connections=new CConnection[MaxConSize];
)的数组,但数组中的元素实际上为空
所以在执行时:if(1==connections[i].status)
它抛出一个NPE
要修复它,请在构造函数中实例化CConnection
对象:
private CConnection[] connections;
public CConnectionManager (){
connections=new CConnection[MaxConSize];
for(int i = 0; i < connections.length; i++){
connections[i] = new CConnection();
}
}
privateConnection[]连接;
公共CConnectionManager(){
连接=新的CConnection[MaxConSize];
对于(int i=0;i
您正在声明一个包含10个CConnection
(connections=new CConnection[MaxConSize];
)的数组,但数组中的元素实际上为空
所以在执行时:if(1==connections[i].status)
它抛出一个NPE
要修复它,请在构造函数中实例化CConnection
对象:
private CConnection[] connections;
public CConnectionManager (){
connections=new CConnection[MaxConSize];
for(int i = 0; i < connections.length; i++){
connections[i] = new CConnection();
}
}
privateConnection[]连接;
公共CConnectionManager(){
连接=新的CConnection[MaxConSize];
对于(int i=0;i
您正在声明一个包含10个CConnection
(connections=new CConnection[MaxConSize];
)的数组,但数组中的元素实际上为空
所以在执行时:if(1==connections[i].status)
它抛出一个NPE
要修复它,请在构造函数中实例化CConnection
对象:
private CConnection[] connections;
public CConnectionManager (){
connections=new CConnection[MaxConSize];
for(int i = 0; i < connections.length; i++){
connections[i] = new CConnection();
}
}
privateConnection[]连接;
公共CConnectionManager(){
连接=新的CConnection[MaxConSize];
对于(int i=0;i
您正在声明一个包含10个CConnection
(connections=new CConnection[MaxConSize];
)的数组,但数组中的元素实际上为空
所以在执行时:if(1==connections[i].status)
它抛出一个NPE
要修复它,请在构造函数中实例化CConnection
对象:
private CConnection[] connections;
public CConnectionManager (){
connections=new CConnection[MaxConSize];
for(int i = 0; i < connections.length; i++){
connections[i] = new CConnection();
}
}
privateConnection[]连接;
公共CConnectionManager(){
连接=新的CConnection[MaxConSize];
对于(int i=0;i