In programming languages, an abstract type is a type in a nominative type system that can be instantiated directly; a type that is not abstract – which can be instantiated – is called a concrete type.

In programming languages, an abstract type is a type in a nominative type system that can be instantiated directly; a type that is not abstract – which can be instantiated – is called a concrete type. A: 正确 B: 错误

Which of the following is false? ( ) A: A static method must be used to access private static instance variables. B: A static method can be accessed even when no objects of its class have been instantiated. C: A static method has no this reference. D: A static method can call instance methods directly.

Which two allow the class Thing to be instantiated using new Thing（）？ A:  public class Thing { } B:  public class Thing { public Thing（） {} } C:  public class Thing { public Thing（void） {} } D:  public class Thing { public Thing（String s） {} } E:  public class Thing { public void Thing（） {} public Thing（String s） {} }