Optional orElse vs orElseGet

StacktraceguruJuly 4th, 2020Last Updated: July 1st, 2020

0 1,008 3 minutes read

Java 8 introduced a fantastic concept of Optional, which we looked into in our blog Java 8 Optional.

So just to give a short recap, Optional is used to represent Optional object or empty value instead null reference. This will help to avoid null pointer exception which occurs when we try to perform some operation on null reference object.

For accessing the value from optional object, there are few methods like get, orELse, orElseGet, etc. Whenever we look at orElse vs orElseGet method, we always get confused. What is the difference and when to use which method?

When we overview these methods, we think that we can use orElse(functionCall()) instead of orElseGet(Class::functionDef), and it will have the same outcome. Then why is there a need to create two different methods? The straight answer is there is difference in the behaviors and they make huge difference in case of performance.

Let us see each of their behavior in detail in this blog.

Syntax of orElse vs orElseGet

OrElse method takes a parameter which will be returned if the optional doesn’t have value.

OrElseGet method needs a function which will be executed to return value if the optional doesn’t have value.

This shows that orElse method needs a value and orElseGet method needs supplier functions.

If we pass function to orElse method it will always be executed to fit the syntax before executing the statement. However, in case of orElseGet method we cannot pass value and the function is executed only if optional doesn’t have value.

Difference: orElse vs orElseGet

We will use following function to get value if optional is null

public String getFunctionForTest() { 
   System.out.println("\n ===== function called ===== "); 
   return "default value"; 
}

Let’s take scenario of Optional object has null value

public void orElseVSorElseGet() {
       Optional<String> optional = Optional.ofNullable(null);
  
       String orElseGetResult = optional.orElseGet( this::getFunctionForTest); 
        System.out.println("value in orElseGetResult " + orElseGetResult); 
  
        String orElseResult = optional.orElse(this.getFunctionForTest()); 
        System.out.println("value in orElseResult " + orElseResult); 
}

Output:

===== function called =====
value in orElseGetResult default value 
 
===== function called =====
value in orElseResult default value

As we can see that the option doesn’t have value and we need to take value form else part. So as expected, the function is called in both cases.

Now let’s take an example where we have the value in optional object and we don’t need to execute else part

public void orElseVSorElseGet() { 
       Optional<String> optional = Optional.ofNullable("value found"); 
 
    String orElseGetResult = optional.orElseGet(this::getFunctionForTest); 
       System.out.println("value in orElseGetResult " + orElseGetResult); 
  
       String orElseResult = optional.orElse(this.getFunctionForTest()); 
        System.out.println("value in orElseResult " + orElseResult); 
}

Output:

value in orElseGetResult default value
 
 ===== function called =====
value in orElseResult default value

As we know that the option object has a value, so we don’t need to take value form else part.

So we expect that function should not be executed. However the function was executed in the case of orElse method.

In the above example we may not notice the performance difference, but when we have complex process to take default value it affects performance. You can consider the example where you need database or network call to take default values it will be slower even if you have value.

In such cases it’s better to use orElseGet method.

In case of orElse, else part is computed even if value is present. If we have default static value then orElse is good choice. If you need a computation logic for default value we should use orElseGet.

Fast track reading

OrElse method in optional takes a parameter
OrElseGet method in optional needs a supplier function
In case of orElse method, else part is computed even if value is present
In case of orElseGet method, else part is computed only if Optional object is empty
For fixed value orElse method should be used
If we need to compute value at run time we should use orElseGet