Filtering a List in Java

Introduction

The main purpose of this tip is to filter any List containing custom instances. Suppose you have a list of 100 Employees and you want a filtered list on the basis of names starting with "John". May be, there are lots of existing ways to implement this. However, I have tried to implement and want to share what I have got.

Implementation

To implement filtering, we need an interface called Filter, which basically carries the filter logic.

interface Filter<T,E> {
    public boolean isMatched(T object, E text);
}

And a FilterList class which returns the FilteredList.

public class FilterList<E> {
    public  <T> List filterList(List<T> originalList, Filter filter, E text) {
        List<T> filterList = new ArrayList<T>();
        for (T object : originalList) {
            if (filter.isMatched(object, text)) {
                filterList.add(object);
            } else {
                continue;
            }
        }
        return filterList;
    }
} 

And here is our simple Employee bean class.

public class Employee  {

    private String name;

    public Employee(String name) {
        setName(name);
    }
    /**
     * @return the name
     */
    public String getName() {
        return name;
    }

    /**
     * @param name the name to set
     */
    public void setName(String name) {
        this.name = name;
    }
}  

Now we have to create our filter first. Here is the FilterListTest class to test the FilterList.

public class FilterListTest {
    public static void main(String main[]) {
        List<Employee> empList = new ArrayList<Employee>();
        //Testing value
        Employee emp = new Employee("John Miller");
        empList.add(emp);
        for (int i = 0; i < 5; i++) {
            emp = new Employee("John Miller");
            empList.add(emp);
            emp = new Employee("Miller John");
            empList.add(emp);
        }
        /**
        ** Creating Filter Logic
        **/
        Filter<Employee,String> filter = new Filter<Employee,String>() {
            public boolean isMatched(Employee object, String text) {
                return object.getName().startsWith(String.valueOf(text));
            }
        };
	/**
	* Pass filter to filter the original list
	*/
        List<Employee> sortEmpList = new FilterList().filterList(empList, filter, "John");
    }
}  

All done. Your Employee list is now filtered with "John".