[JAVA] [For our newcomers] About isXXX methods

For example, isXXX methods?

There are ʻisFile and ʻisDirectory methods of the File class. File class official document

feature is?

It simply returns a boolean. boolean is a data type that represents a boolean value such as true or false. It can be used as a branch condition for ʻif statementsand as a continuation condition forwhile statements`.

code example of isXXX method

As an example, let's create the ʻisBlank` method.

isBlank

//Determines if the specified value is an empty string.
//True if empty string.
//Otherwise it returns false.
public boolean isBlank(String value) {
  if (value.isEmpty()) {
    return true;
  }

  return false;
}

How to use?

The code is shown using the ʻis Blank` created earlier as an example.

First is the ʻif statement`.

Used as a branch condition

if (isBlank(value)) {
  //Processing when no characters are entered
  System.out.println("No characters have been entered.");
} else {
  //Processing when characters are entered
  System.out.println("The entered characters are "" + value + ""is.");
}

ʻIf (isBlank (value))` By writing like this, You can clearly convey to the reader the intent that "if no value has been entered".

Next is the while statement. ! Is Blank is used to invert true and false.

Use as a continuation condition

while (!isBlank(value)) {
  //Processing when characters are entered
  System.out.println("The entered characters are "" + value + ""is.");
}

It is while (! IsBlank (value)). As with the ʻif statement`, the intent is clear if a value has been entered.

value.isEmpty () is fine

It's not a mistake. However, the definition of blank can change from time to time. The previous ʻis Blank` only determines whether it is an empty string.

What if the argument is null? If you make a method call to null, you will get an exception.

//java if the content of value is null.lang.NullPointerException occurs
value.isEmpty()

Corresponds to null

By making the empty string judgment process a method, you can easily handle null. Now, let's actually make ʻis Blank correspond to null`.

isBlank

//Determines if the specified value is null or an empty string.
//True if null or empty string.
//Otherwise it returns false.
public boolean isBlank(String value) {
  if(value == null) {
    return true;
  }

  if(value.isEmpty()) {
    return true;
  }

  return false;

  //You can write as follows, but it is for newcomers.
  // return value == null || value.isEmpty();
}

I just added the following logic to ʻisBlank`.

Added line

  if(value == null) {
    return true;
  }

In this way, you can apply the changes to all the places that call ʻisBlankby making only one modification. It's okay to say thatblank also includes null` when you've finished writing the code and are about to test it.

Summary

Someone else may take care of the code tomorrow, a week later, or a year later. If you put together the processing like this, it will be easier later.