Question

所以我在SwingWorker中有了forCancelled的代码

boolean isCancelled() return true;

它给我错误

尝试分配较弱的访问权限;是公共错误

我不知道如何修复它。谁能帮我？谢谢

Answer 1

首先，你需要在方法体周围使用大括号。

其次，您当前声明它的方式使用包访问权限，但isCancelled方法是公开的，因此您必须使用其他公共方法覆盖它。

第三，该方法无论如何都是final，所以你不能首先覆盖它。目前尚不清楚你想要达到的目标，但这不是可行的方法。

Answer 2

你可以像以前的海报一样试试这个：

Connecting

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet sent successfully to the server was 0 milliseconds ago. The  driver has not received any packets from the server.

    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
    at java.lang.reflect.Constructor.newInstance(Unknown Source)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:389)
    at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1038)
    at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:338)
    at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2237)
    at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2270)
    at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2069)
    at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:794)
    at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:44)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
    at java.lang.reflect.Constructor.newInstance(Unknown Source)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:389)
    at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:399)
    at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:325)
    at java.sql.DriverManager.getConnection(Unknown Source)
    at java.sql.DriverManager.getConnection(Unknown Source)
    at PROKOM.Zadanie11.test.main(test.java:23)
Caused by: java.net.ConnectException: Connection refused: connect
    at java.net.DualStackPlainSocketImpl.connect0(Native Method)
    at java.net.DualStackPlainSocketImpl.socketConnect(Unknown Source)
    at java.net.AbstractPlainSocketImpl.doConnect(Unknown Source)
    at java.net.AbstractPlainSocketImpl.connectToAddress(Unknown Source)
    at java.net.AbstractPlainSocketImpl.connect(Unknown Source)
    at java.net.PlainSocketImpl.connect(Unknown Source)
    at java.net.SocksSocketImpl.connect(Unknown Source)
    at java.net.Socket.connect(Unknown Source)
    at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:213)
    at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:297)
... 15 more

但是你可能还想考虑一下你是否真的需要一个方法，当你可能只需要一个变量时：

@Override
public boolean isCancelled(){
 return true;
}

Answer 3

因为如果覆盖方法，您在超类或扩展中使用相同的访问权限（package - ＆gt; protected - ＆gt; public）。

如果超类的例子：

boolean isCancelled(){}; // package local default access

protected boolean isCancelled(){};

public boolean isCancelled(){};

在子类中使用（相对）：

@Override
boolean isCancelled(){}; //or add  protected or public

@Override
protected boolean isCancelled(){};//or change public

@Override
public boolean isCancelled(){};

试图分配较弱的访问权限;是isCancelled的公共错误

3 个答案: