Runtime environment (short for Java Runtime Environment)

Jdk: Java development toolkit. JDK is the core of the whole JAVA, including Java runtime environment and a bunch of Java tools (javac/java/jdb, etc. ) and Java-based class libraries (that is, Java API? Including rt.jar).

Steps: first compile the class file with javac, and then run the class file with java.

Decimal, octal and hexadecimal forms; Add l after the number, such as 3333L.

Decimal form, scientific counting form; Just express it in decimal form, such as 33.33.

For example,? int[]arrayB = new int[5]；

For example, int [] [] array = new int [1] [5];

While (if the conditions are met, continue execution; If not, exit)

Do ... while (quit until the conditions are not met)

for(； ; ) (Continue execution if conditions are met, and exit if conditions are not met)

Break the whole cycle; Continute jumps out of the single-layer loop

I don't quite understand what this means. The description of a class can be annotated with/* */

Class initializes the called method. By default, the class is constructed with or without parameters. You can also define your own parameterized constructor.

Public class * * *

Abstract abstract class

Final category modifier final

Interface interface

Class default access controller (can only be called by the same package)

The most essential difference is that the interface is a highly abstract template, while abstract classes provide some abstract methods for subclasses to implement concretely. Others are very different. Search online by yourself.

Abstract, this class adds this modifier. You can let subclasses implement abstract methods according to specific situations to adapt to different scenarios (you can probably search for specific functions)

Try ... catch it and you can scream.

There are eight, right?

Java.lang package, java.util package, java.io package, java.net package, java.sql package, java.awt package, javax.swing package, java.text package.

String function, which can manipulate and store strings. . . ; trim()，equal()，subString() ......

Java.util.Vector provides a Vector class to implement functions similar to dynamic arrays.

One thing I can think of is that vectors can be dynamically resized, and the size of arrays cannot be changed after definition.

Classes that manipulate text; isExist()，delete()，getName()

Read with io stream

2 1 ~ 27. I don't know much about the graphical interface of Java. Check it yourself. Can you find it?

28.

Uniform resource locator? (uniform? Resources? Locator? Website)

Is an identification method to completely describe the addresses of web pages and other resources on the Internet.

Every web page on the Internet has a unique name identification, usually called URL address.

Socket programming has not been used yet.

30.？ ① Load the database driver;

② Establish database connection through JDBC;

③ Access the database and execute SQL statements;

④ Disconnect the database.

Everyone, I hope it can help you.