Are interfaces a valid substitute for utility classes in Java 8? [duplicate]

Answer 1

You should not use interface. Interfaces cannot have private constants and static initializers.

public class Utility {

    private Utility() {}

    public static final Map MAP_CONSTANT;
    static {
        Map map = new HashMap<>();
        map.put("zero", 0);
        map.put("one", 1);
        map.put("three", 3);
        MAP_CONSTANT = Collections.unmodifiableMap(map);
    }

    private static String PRIVATE_CONSTANT = "Hello, ";

    public static String hello(String name) {
        return PRIVATE_CONSTANT + name;
    }
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