CODEWITHSUNDEEP
javafor-looparraylistjava-7
Hars
Hars

Reputation: 169

How to count the nested list elements size using Java 7?

I have a Object which contains a list of another object which contains a list of another object and so on... suppose I want to get count of nested list elements(lets say last one), what should be best approach rather than using traditional for loop in java as I have done in below example - 

public static void main(String[] args) {

    Statement statement = new Statement();
    statement.getInvAccount().add(new InvestmentAccount());
    statement.getInvAccount().get(0).getSecAccountStmt().add(new SecurityStatement());
    statement.getInvAccount().get(0).getSecAccountStmt().get(0).getTransactionStatement().add(new TransactionStatement());
    statement.getInvAccount().get(0).getSecAccountStmt().get(0).getTransactionStatement().add(new TransactionStatement());
    statement.getInvAccount().get(0).getSecAccountStmt().get(0).getTransactionStatement().add(new TransactionStatement());

    // method to count the number of TransactionStatement
    System.out.println("Size of TransactionStatement is : " + count(statement));

}

private static int count(Statement stmt) {
    int countOfTransStmt = 0;
    for (InvestmentAccount invAcc : stmt.getInvAccount()) {
        if (invAcc != null) {
            for (SecurityStatement secStmt : invAcc.getSecAccountStmt()) {
                if (secStmt != null) {
                    countOfTransStmt = countOfTransStmt + secStmt.getTransactionStatement().size();
                }
            }
        }
    }
    return countOfTransStmt;
}

Upvotes: 3

Views: 2219

Answers (1)

John Kugelman
John Kugelman

Reputation: 361729

In Java 7 you're not going to do better than two for loops. I wouldn't bother with anything different.

In Java 8 you can use streams to flatten it out:

private static int count(Statement stmt) {
    return stmt.getInvAccount().stream()
        .filter(Objects::nonNull)
        .flatMap(InvestmentAccount::getSecAccountStmt)
        .filter(Objects::nonNull)
        .flatMap(SecurityStatement::getTransactionStatement)
        .count();
}

I would encourage you to get rid of the null checks. If you're going to ignore nulls, better to just expect them not to be inserted in the first place. It'll get rid of a lot of extra if checks throughout your code, I expect.

I'd also encourage you not to abbreviate your variables and methods. Spell out "statement" and "investment" and the like. The abbreviations are harder to read and the brevity isn't really a win.

Similarly, try to use more descriptive method names. countTransactions is better for the main method. And for the various getters, methods that return lists ought to be plural: "getAccounts" rather than "getAccount". Notice how the getters now match the class names; if you know the class name, you know the getter name. You don't have to guess if one or the other is abbreviated:

private static int countTransactions(Statement statement) {
    return statement.getInvestmentAccounts().stream()
        .flatMap(InvestmentAccount::getSecurityStatements)
        .flatMap(SecurityStatement::getTransactionStatements)
        .count();
}

Upvotes: 2

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