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Avoid Using Wildcard Imports in Java

Medium
maintainabilityreadability

What is it?​

This practice is triggered by the use of wildcard imports in Java, which can make code less readable and harder to maintain due to ambiguities in class usage.

Why apply it?​

Wildcard imports reduce code readability and can introduce conflicts when class names overlap, posing difficulties in understanding where a class originates from. It helps avoid potential issues during dependency upgrades or Java version migrations.

How to fix it?​

Replace wildcard imports with explicit class imports to maintain code clarity and avoid conflicts.

Examples​

Example 1:​

Negative​

This negative example uses wildcard imports, making it unclear which Date class is being used.

import java.sql.*;  // Noncompliant
import java.util.*; // Noncompliant

public class DatabaseUtility {
    private Date date;
    private List<String> dataList = new ArrayList<>();
    
    public void addData(String data) {
        dataList.add(data);
    }

    // Additional logic for the utility
}

Example 2:​

Positive​

This positive example explicitly imports required classes to clearly establish where each class is sourced from.

import java.sql.Date;
import java.util.List;
import java.util.ArrayList;

public class DatabaseUtility {
    private Date date;
    private List<String> dataList = new ArrayList<>();

    public void addData(String data) {
        dataList.add(data);
    }

    // Additional logic for the utility
}

Negative​

The negative example uses wildcard imports, which could lead to ambiguity in large projects.

import java.util.*; // Noncompliant

public class ConfigurationReader {
    private Map<String, String> configMap = new HashMap<>();

    public void addConfig(String key, String value) {
        configMap.put(key, value);
    }

    public String getConfig(String key) {
        return configMap.get(key);
    }

    // Other configuration related methods
}

Example 3:​

Positive​

The positive example details the classes needed explicitly, enhancing readability and avoiding import conflicts.

import java.util.Map;
import java.util.HashMap;

public class ConfigurationReader {
    private Map<String, String> configMap = new HashMap<>();

    public void addConfig(String key, String value) {
        configMap.put(key, value);
    }

    public String getConfig(String key) {
        return configMap.get(key);
    }

    // Other configuration related methods
}