Access control of the package: subclass in the same bag in different packages public y yprotect y y NPRIVATE N N n
I / O and four abstract classes read and write bytes: InputStream OutputStream reads and writes unicode characters: Reader Writer
IteratraRrayList VectorhashSettreesetHashmap Treemap
JDBC database URLString url = "jdbc: odbc: mydb"; establishing a connection DriverManager Connection con = DriverManager.getConnection (url, "user", "pass"); to create a Statement object Statement stmt = con.createStatement (); String sql = " Select * from users "; execution query Result = stmt.executeQuery (SQL); while (rs.next ()) {...}
Equal and toString method in the Object class .Equal is used to test whether an object is equal to another object. TOSTRING returns a string representing the object, almost every class overloads the method to return the correct representation of the current state. (TSTRING method is a very important method)
