SeparationOfConcernsLambda.java

  public static int totalAssetValues(final List<Asset> assets,
    final Predicate<Asset> assetSelector) {
    return assets.stream()
                 .filter(assetSelector)
                 .mapToInt(Asset::getValue)
                 .sum();
  }
  
  public static void main(final String[] args) {
    List<Asset> assets = Arrays.asList(
      new Asset(Asset.AssetType.BOND, 1000),
      new Asset(Asset.AssetType.BOND, 2000),
      new Asset(Asset.AssetType.STOCK, 3000),
      new Asset(Asset.AssetType.STOCK, 4000)
    );

    System.out.println("Total of all assets: " + 
      totalAssetValues(assets, asset -> true));

    System.out.println("Total of bonds: " + 
      totalAssetValues(assets, asset -> asset.getType() == AssetType.BOND));

    System.out.println("Total of stocks: " + 
      totalAssetValues(assets, asset -> asset.getType() == AssetType.STOCK));
  }