How do I use for-each to iterate generic collections?

In this example you will learn you to iterate a generic collection using the for-each loop. There was actually no for-each keyword or statment in Java. It just a special syntax of the for loop. The structure or syntax of the for-each loop is as follow.

for (type var : collections) {
    body;
}

This form of for loop is always read as foreach and the colon (:) character is read as “in”. Given that definition, if the type is a String you will read the syntax above as “foreach String var in collections”. The var in the statement above will be given each value from the collections during the iteration process.

Let’s compare two codes, the first one that use a generic and another code that doesn’t use a generic so we can see the difference from the iteration perspective when working with a collection.

package org.kodejava.example.generics;

import java.util.ArrayList;
import java.util.List;

public class ForeachGeneric {

    public void loopWithoutGeneric() {
        List customers = new ArrayList();
        customers.add(new Customer());
        customers.add(new Customer());
        customers.add(new Customer());

        for (int i = 0; i < customers.size(); i++) {
            Customer customer = (Customer) customers.get(i);
            System.out.println(customer.getFirstName());
        }
    }

    public void loopWithGeneric() {
        List<Customer> customers = new ArrayList<>();
        customers.add(new Customer());
        customers.add(new Customer());
        customers.add(new Customer());

        for (Customer customer : customers) {
            System.out.println(customer.getFirstName());
        }        
    }
}

What you see from the code snippet above is how much more clean our code is when we are using the generic version of the collection. In the first method, the loopWithoutGeneric we have to manually cast the object back to the Customer type. But in the second method, the loopWithGeneric method, no cast is needed as the collection will return the same type as what the collection was declared to hold.

Wayan

Programmer, runner, recreational diver, live in the island of Bali, Indonesia. Mostly programming in Java, Spring Framework, Hibernate / JPA. Support me by donating.

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