I learned how to create the correct method in the exercises in the summary of Chapter 5. If there is a return value, use the return type instead of void. Define the value to be returned before return in the method and then return it to the return value.
The finished Java program is a collection of multiple class files, so it is not created with a single class file. So if you want to distribute it to someone, you need to pass all the class files
When calling a method from another class, call it with class name.method name ()
There is no parent-child relationship or hierarchical relationship in the package, and the default package is specified for the class without the package statement and cannot be imported by the import statement. When calling a method from another package, write "affiliation package name.class name.method name" = This is called FQCN (fully limited class name)
If you want to omit the input of FQCN, add an import statement .. Basically, in Java, you can always use all the classes that the JVM can handle without making any declarations.
By importing and using API (convenient function), it is possible to save time and create a large program. You can refer to the API reference on the site
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