Java – Boolean return of set.add() in if conditional

clean codecoding-stylejava

The add operator of the set class returns a boolean which is true if the element (which is to be added) wasn't already there, and false otherwise. Is writing

if (set.add(entry)) {
    //do some more stuff
}

considered good style in terms of writing clean code?
I am wondering since you do two things at once. 1) adding the element and 2) checking whether the element existed.

Best Answer

Yes, it is.

The usual point of having an operation return a Boolean value is that you can use it to make decisions, i.e. within an if construct. The only other way you could realize this potential would be to store the return value in a variable and then immediately reuse it in an if, which is just silly and certainly not in any way preferable to writing if(operation()) { ... }. So just go ahead and do that, we won't judge you (for that).

Related Solutions

Java – Why is the hashCode method usage of HashSet not specified in the API

in the documentation of hashcode itself:

Returns a hash code value for the object. This method is supported for the benefit of hash tables such as those provided by HashMap.

The general contract of hashCode is:

Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer, provided no information used in equals comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application.

If two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result.

It is not required that if two objects are unequal according to the equals(java.lang.Object) method, then calling the hashCode method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hash tables.

not that I can find, but hashcode is specifically there for the support of hash tables as said in the documentation.

Java – Is throwing an exception an anti-pattern here

Yes, your colleague is right: that is bad code. If an error can be handled locally, then it should be handled immediately. An exception should not be thrown and then handled immediately.

This is much cleaner then your version (the getValueByKey() method is removed) :

public String getByKey(String key) {
    if (valuesFromDatabase.containsKey(key)) {
        return valuesFromDatabase.get(key);
    } else {
        String defaultValue = defaultValues.get(key);
        valuesFromDatabase.put(key, defaultvalue);
        return defaultValue;
    }
}

An exception should be thrown only if you do not know how to resolve the error locally.

Best Answer

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Java – Why is the hashCode method usage of HashSet not specified in the API

Java – Is throwing an exception an anti-pattern here

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