How to create a mutable array list containing immutable objects, Java

Question

I have objects representing columns in a table that I want to declare as final. Some of these columns represent primary keys in my table, and for those columns I want to add them to an array list that gets passed into a function.

How can I declare a mutable list (one that I can add primary key columns to) that contains immutable objects (the column objects themselves)?

Make the objects immutable by using private and final, then add them into Arraylist — Rishi
– Rishi, Commented Sep 12, 2016 at 23:17
@Rishi When I declare the array list, is there a way to know that it will contain immutable objects? Something like ArrayList<final Column> — Adam
– Adam, Commented Sep 12, 2016 at 23:21
So - your Column class implementation will need to declare all of its fields as final and only provide getters. Simply declaring a reference to your Column class as final isn't sufficient. — Michael Krause
– Michael Krause, Commented Sep 12, 2016 at 23:23

Rishi · Accepted Answer · 2016-09-12 23:30:50Z

2

public final class Column {

private final Integer a;
private final String  b;

public Column(Integer a, String b) {
    this.a = a;
    this.b = b;
}

public Integer getA() {
    return a;
}

public String getB() {
    return b;
}

}

Create column class in this fashion and then add the object to ArrayList. Check this out : http://docs.oracle.com/javase/tutorial/essential/concurrency/imstrat.html

answered Sep 12, 2016 at 23:30

Rishi

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