PECS (Producer-Extends, Consumer-Super) is a principle used in the Java programming language to work with types in parameterized classes and methods. The main idea of PECS is to correctly define and use types as arguments to ensure type safety during compilation and prevent runtime errors. To understand the concept of PECS more fully, let's take a closer look at it.
PECS allows us to control the operations that can be performed on collections of parameterized types. This principle is based on two simple rules:
1. If a type is used as a producer of elements, the "extends" keyword should be used. A producer provides elements that can be read but cannot be modified.
2. If a type is used as a consumer of elements, the "super" keyword should be used. A consumer accepts elements that can be modified but cannot be read.
Let's look at some code examples to better understand how PECS works.
Example 1: Producer (extends)
```java
public class ProducerExample {
public static void copyElements(List source, List destination) {
for (Number number : source) {
destination.add(number);
}
}
public static void main(String[] args) {
List integerList = Arrays.asList(1, 2, 3);
List