java - variable object properties in a loop

Question

I know how to do this in PHP so I'm hoping I can do it in Java as well. Here is some of my Java code:

String curYear = form.getCurYear();
if(curYear == null || curYear.length() == 0 || !curYear.matches(decimalRegex)) {
  errors.rejectValue("curYear", "supplier.curYear.invalid", "Invalid format for dollar amount");
}

String lastYear = form.getLastYear();
if(lastYear == null || lastYear.length() == 0 || !lastYear.matches(decimalRegex)) {
  errors.rejectValue("lastYear", "supplier.lastYear.invalid", "Invalid format for dollar amount");
}

These 2 chunks are followed by several more almost identical chunks where just the variable names/strings change. So I wanted to create a for(or foreach) loop to create all these using an array of the variable names. But for the form.getCurYear(); code, the first character of the variable name(curYear) is capitalized, so I would need to construct the variable name beforehand. Easy enough: String capField = inputField.substring(0, 1).toUpperCase() + inputField.substring(1);

Now how do I use that variable name in the form property call? I know form.capField() won't work. Is this even possible?

tom · Accepted Answer · 2018-09-14 19:15:40Z

4

You could Java 8 Supplier to do something like this:

validate(form::getCurYear, "curYear", decimalRegex, errors);
validate(form::getLastYear, "lastYear", decimalRegex, errors);

And your validate method could look like this:

private static void validate(Supplier<String> method, String name, String decimalRegEx, Errors errors) {
    String val = method.get();
    if (val==null || val.length()==0 || !val.matches(decimalRegEx)) {
        errors.rejectValue(name, "supplier." + name + ".invalid", "Invalid format for dollar amount");
    }
}

You could declare decimalRegex and errors as globals or class members to shorten the signature of validate.

answered Sep 14, 2018 at 19:15

tom

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Comments

Ashraff Ali Wahab · Accepted Answer · 2018-09-14 19:09:58Z

3

You can do this

    Map<String,String> map = new HashMap<String,String>();

    map.put("curYear", form.getCurYear());      
    map.put("lastYear", form.getLastYear());

    for (Map.Entry<String, String> entry : map.entrySet()) {
        String key = entry.getKey();
        String value = entry.getValue();

        if(value == null || value.length() == 0 || !value.matches(decimalRegex)) {
              errors.rejectValue(key, "supplier"+key+".invalid", "Invalid format for dollar amount");
        }          
    }

This creates the map of name and value and use the value for checking and name for printing.

answered Sep 14, 2018 at 19:09

Ashraff Ali Wahab

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3 Comments

Maxim Over a year ago

Why HashMap is needed here? Better to place strings into two arrays and loop through ones

Ashraff Ali Wahab Over a year ago

Readability. With arrays if we have 20 variables, I have count manually where I have to place the key and value.

Maxim Over a year ago

Didn't get the point. HashMap needed when value retrieved by key.

Code-Apprentice · Accepted Answer · 2018-09-14 19:04:36Z

1

In Java, variable names are only available at compile time. One way to do something like what you want here is to use a Map with the name as a key. You might also be able to do create a solution using a class.

edited Sep 14, 2018 at 19:04

answered Sep 14, 2018 at 19:03

Code-Apprentice

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5 Comments

Code-Apprentice Over a year ago

@dmikester1 After looking more closely at your code, you should also consider putting the duplicated code into a method which you can call with different values.

dmikester1 Over a year ago

So my method would be something like this? private static checkField(String input, String capInput)

Code-Apprentice Over a year ago

@dmikester1 Yes, something like that will probably work.

dmikester1 Over a year ago

Then I run into the same issue of how do I call form.capInput()?

Code-Apprentice Over a year ago

@dmikester1 I don't understand. What is form? How is it declared? And what does capInput() do?

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