Java Learning Notes (i)

1.1.an algorithm for number inversion

A take the reverse,~a=-(a+1). As

~5=-6,~(-8)=7

1.2. access control characters for classes in Java

(the modifier for a class has public,default,abstract,final, The modifiers for the method are public,default,protected, Private)

Public: This class can be accessed by an external package

Default(Default): This class can only be accessed by this package

Protected: This class can only be accessed by the quilt class

Private: This class cannot be accessed by any class

1.3.the difference between static and non-static methods

static methods do not need to create an instance of the class to be used, and a non-static method must create an instance of the class to be used, that is , the new object, and the method is called through the object

1.4.Static Variables

Static variables are static storage and must be defined outside the function, and after being called by a dynamic function, the static variable is the value after the change. Does not return to the initialized value because the function call ends. Such as:

Package Hello;

public class hello{

static int a=1;

int fun (int n) {

A=a*n;

Returm A;

}

public static void Main (string[] args) {

Hello h=new hello ();

for (int i=1;i<4;i++)

System.out.println (H2.fun (i));

}

}

}

1.1.Interfaces and Classes

multiple inheritance properties are forbidden in the Java programming language, but can be used to help extend the method through an interface. A large number of solid and methods can be defined in the interface. But the method is only a declaration, there is no specific implementation, the use of the interface classes themselves have implemented these methods. The difference between an interface and a = class is that:

(1) There is no declaration of variables, but can be defined as solid;

Only the declaration of the method, there is no implementation of the method.

Java Learning Notes (i)