您已经用了两个公共类即公共类MainActivity延伸活动{} 和公共类ConnectedThread继承Thread {} 。但在Java中应该有一个公共类和一个JavaClass中的文件任意多个其他类。所以删除公共类ConnectedThread继承Thread {} 从该文件并创建一个新的Java类：公共类ConnectedThread继承Thread {} 在同一个包。

You have used two public classes i.e public class MainActivity extends Activity{} and public class ConnectedThread extends Thread {}. But in Java there should be one public class and any number of other classes in one JavaClass file. So remove public class ConnectedThread extends Thread {} from that file and create a new Java class: public class ConnectedThread extends Thread {} in the same package.