CODEWITHSUNDEEP
javaloopsfor-loop
Griffin Bender
Griffin Bender

Reputation: 177

for each loop of objects of specific instances in Java

I'd like to have a for each loop to loop through an array of objects.. but only the objects that are an instance of a specific class. To be more clear of what I mean, I've included the example below...

//Declare a list of employee objects
List<Employee> employees = new ArrayList<Employees>;

//Create some employees...
Employee employee = new Employee();
//The class EmployeeExtender extends and is a child of Employee 
EmployeeExtender employeeExtended = new EmployeeExtender(); 

//Now add all the employees, even the ones of different instances to the list
employees.add(employee);
employees.add(employeeExtended);

Now I would like to introduce a for each loop that loops through the employees list that only loops through employees that are an instance of EmployeeExtender. I could just loop through each one and use an if statement (as shown below) but I would like to know if there was a way without making a seperate list to do this.

//I would like to only loop through employees that are an instance of EmployeeExtender
for(Employee employee : employees){
    //I would like to not have this if statement...
    if(employee instanceof EmployeeExtender){
        //do logic...
    }
}

Are my only options creating separate lists, or using the if statement? I'd like to know if there are more options. Thanks.

Upvotes: 1

Views: 1118

Answers (2)

Dawood ibn Kareem
Dawood ibn Kareem

Reputation: 79875

One option that hasn't been considered is to dispatch the logic to an empty method, that's overridden in the subclass you're interested in. I don't think I'd recommend doing it this way, but you did ask for options other than the straightforward for-each / instanceof way of doing it.

public class Employee {
    public void doTheLogic(TheClassYoureCallingFrom caller) {
    }
}

public class EmployeeExtended extends Employee {
    @Override
    public void doTheLogic(TheClassYoureCallingFrom caller) {
        // The actual logic goes here.
    }
}

public class TheClassYoureCallingFrom {

    List<Employee> employees = new ArrayList<Employees>;

    public void theMethodYoureCallingFrom() {
        for (Employee employee : employees) {
            employee.doTheLogic(this);
        }
    }
}

Of course, if you're not using any of the methods of the calling class, there's no need to pass it as a parameter.

Upvotes: 3

Trigary
Trigary

Reputation: 431

You could use Streams:

employees.stream()
    .filter(employee -> employee instanceof EmployeeExtender)
    .forEach(employee -> {
        //do logic
    });

Upvotes: 1

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