Computer level two java review, cramming before the exam

database:

Selection operation refers to the condition where a = ?

The projection operation refers to specifying several attributes, that is, the selection attributes such as select a, b, xxx! ——>Easy to confuse with selection

A natural join is union for columns and intersection for rows!

java is 16 bit unicode

It is equivalent to shifting 1000 to the right by two places and becoming 0010, so it is 2!

Input and output must be io stream

Values ​​of basic data types in java:

In java, it is passed by value, which is a copy of the value, not the original variable! ! !

setLayout(new BorderLayout());

Container container = getContentPane();//The getContentPane() method in JFrame can generate a container object

JOptionPane.showMessageDialog( null, output, “abc”, JOptionPane.INFORMATION_MESSAGE );

Console input:

Scanner scan = new Scanner(System.in);

scan.nextInt();