Solution.java

import org.junit.Test;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

import static org.fest.assertions.Assertions.assertThat;

public class Solution {

    @Test
    public void test() {
        final Foo foo = new Foo();

        foo.setStrings(Arrays.asList("a", "b", "c"));

        foo.setStrings(foo.getStrings());

        assertThat(foo.getStrings()).contains("a", "b", "c");
    }

    static class Foo {

        private final List<String > blas = new ArrayList<String>();

        public List<String> getStrings() { return Collections.unmodifiableList(new ArrayList<String>(blas)); }

        public void setStrings(List<String> blas) {
            if (blas != null) {
                this.blas.clear();
                this.blas.addAll(blas);
            }
        }
    }
}