Basics of Java used in J2ME:
1. Java syntax basics: including basic data types, keywords, operators, etc.
2. Object-oriented thinking: concepts of classes and objects, inheritance and polymorphism, etc.
3. Exception handling
4. Multi-threading
Java basics that are not used in J2ME:
1. Use of javac and java commands in JDK
2. Many classes in Java basics do not have them in J2ME, or the methods in the classes have been greatly simplified. Therefore, it is recommended to be familiar with class libraries in J2ME.
3. Knowledge such as Applet, AWT, and Swing cannot be used in J2ME at all.
2. Functions that cannot be completed temporarily in J2ME
I will list some functions that cannot be completed in J2ME for the time being. I hope everyone can actively add them:
1. Do not change the code in the mobile phone to implement porting, mainly referring to games.
2. Dynamically modify the button text.
3. Accept Chinese input on Canvas.
4. Operate local resources, such as address books, received short messages, etc.
5. Create destructive mobile phone viruses.
3. Cross-platformity of J2ME
J2ME technology originates from Java, so it also has the advantages of JVM and can be ported on platforms that support Java. However, the current J2ME technology does a bad job on cross-platforms. Let’s take a brief look at the reasons:
1. The screen sizes of the mobile phone are different:
This is mainly in interface production. If you are using an advanced user interface, such as application development, user login, user registration, etc., there are generally no problems.
If you are using a low-level user interface, such as if you are building a game, then you need to consider this issue.
I have said so much in a nutshell. I hope that friends who study J2ME can avoid detours. I hope everyone will actively correct and supplement the shortcomings. Thank you for your support!