如何从另一个类访问ArrayList

Question

I'm trying to find a way to copy the contents from an ArrayList in a class of mine to the class I am currently working in.

This is how my code is currently looking in the class I want the contents to be transferred to:

            MainActivity MA = new MainActivity();
    ArrayList<String> deletedValues = new ArrayList<String>();
    for(String item :MA.deletedItems){
        deletedValues.add(item);
    }

Also, the ArrayList in the MainActivity has the modifier private if that matters

The code above does not cause any errors but will not return any values to the new ArrayList, deletedValues.

Answer 1

You can make a get method in whatever class contains the arraylist like so:

public ArrayList getDeletedValues() {
    return deletedValues;
}

That is how you normally access private variables.

Answer 2

Have a look at the Getters and Setters design pattern. It means you can have your variables private whilst providing access to them for other classes in a manner you can control. Generally a typical class using getters and setters would look a little like this:

public class MyClass {
    private int myInt;

    // Setter
    public void setMyInt(int value) {
        myInt = value;
    }

    // Getter
    public int getMyInt() {
        return myInt;
    } 
}

When implemented in context you gave, you can expect your code to look similar to this, with your getters and setters in the MainActivity class looking like the above example.

MainActivity MA = new MainActivity();
ArrayList<String> deletedValues = new ArrayList<String>();
for(String item :MA.getDeletedItems()){
    deletedValues.add(item);
}

However I will take this opportunity to point out that rather than creating a new instance of your MainActivity class, you would probably find it much more beneficial to pass the current instance of the MainActivity class to the class you are using through the means of a constructor or similar.