Shopping cart program in Java with a text menu
Naming
I can't begin with another topic.
You use 2 different approaches to name your variables:

someName -&gt; it's a camelCase
some_name -&gt; it's a snake_case

Read this article to understand the difference
Java has own code style and you should use only camelCase for your variable name, class name, method name
I'll provide more examples about naming in Java.
Let's start with simple variable (not final, because final variable has own name convention)

someName - for variable (not final variable) name
someMethod - for method name
SomeClass - for class name

You may have final variable, it's commonly use in case when you need the property that will be general for all objects of the class and this property will not change.
private static int SOME_IMMUTABLE_VARIABLE = 10;

You need to fix names for your variables and methods:
remove_keychains -&gt; removeKeyChains() // in the same manner for others