Convert List of String to List of BigDecimal in java

Question

I'm facing a problem in converting a list of String to list of Bigdecimal in java.

I have a List of String like,

List<String> stringList = new LinkedList<String>();
stringList.add("123");
stringList.add("456");
stringList.add("789");

and BigDecimal List as

List<BigDecimal> bigDecimalList = new LinkedList<BigDecimal>();

Now I want to convert stringList to bigDecimalList . I know we can iterate through the stringList and can add to bigDecimalList using new BigDecimal(string) . Is there any other work around than looping???

Any help is appreciated. Thanks.

Answer 1

Well something's got to loop - and until Java 8 comes with lambda expressions to make it easier to express the conversion, there's no general purpose way of doing the conversion. Obviously you could write a method which took the class name and always passed each element of the incoming list as an argument to the constructor of the target class via reflection, but that would fail in all kinds of other situations.

Given how short the loop is, I'd definitely do that:

List<BigDecimal> bigDecimalList = new LinkedList<BigDecimal>();
for (String value : stringList) {
    bigDecimalList.add(new BigDecimal(value));
}

Do you really need to avoid those 4 lines of code?

Answer 2

At some level - either in an external library, a lower level library, or in your code - you'll have to iterate over the structure and create new BigDecimal objects in your other list.

Now that Java 8 is effectively out, it can be expressed rather tersely as thus. This code assumes that you already have stringList defined somewhere.

List<BigDecimal> bigDecimalList = stringList.stream()
        .map(BigDecimal::new)
        .collect(Collectors.toList());

This takes all of the contents of the stringList , maps them across to the constructor of BigDecimal , and collects them into a new List object, which we then assign.

Answer 3

Use Google Common's transform . You supply the original list and the transform function, and it does the looping, applying the transform to each element. This is actually done lazily, so the transforms aren't applied until you iterate or get the elements.

List<String> strings = ...
List<BigDecimal> numbers = Lists.transform(strings, new Function<String, BigDecimal>() {
  public BigDecimal apply(String str) {
    return new BigDecimal(str);
  }
});

Doing this will move you one step closer to functional programming.

Answer 4

If you use Eclipse Collections (formerly GS Collections) and change stringList to a MutableList or something similar, you can write:

MutableList<String> stringList = FastList.newListWith("123", "456", "789");

MutableList<BigDecimal> bigDecimalList = stringList.collect(new Function<String, BigDecimal>()
{
    public BigDecimal valueOf(String eachString)
    {
        return new BigDecimal(eachString);
    }
});

With Java 8 method references, this becomes:

MutableList<BigDecimal> bigDecimalList = stringList.collect(BigDecimal::new);

Note: I am a committer for Eclipse Collections.