Avoid using specific implementation types

Metadata

ID: java-best-practices/loose-coupling

Language: Java

Severity: Notice

Category: Best Practices

Description

Relying on particular implementation types, such as, HashSet or LinkedList can limit your adaptability to embrace alternative implementations in the future, particularly as your requirements change and your code needs to undergo changes.

It is recommended to opt for general types such as Set or List when declaring variables and parameters.

Non-Compliant Code Examples

import java.util.ArrayList;
import java.util.HashSet;
import java.util.HashMap;

public class Foo {
    private ArrayList<SomeType> list = new ArrayList<>();

    public HashSet<SomeType> set = new HashSet<SomeType>();

    public HashMap<SomeType> getMap() {
        return new HashMap<SomeType>();
    }    
    public String foo(HashMap<String, String> map) {
        return map.get("foo");
    }
}

Compliant Code Examples

import java.util.ArrayList;
import java.util.HashSet;
import java.util.HashMap;

public class Foo {
    private List<SomeType> list = new ArrayList<>();

    public Set<SomeType> set = new HashSet<SomeType>();

    public Map<SomeType> getMap() {
        return new HashMap<SomeType>();
    }
    public String foo(Map<String, String> map) {
        return map.get("foo");
    }
}