Java判断map是否为null或者空的方法小结

import java.util.HashMap;  
import java.util.Map;  
  
public class MapNullOrEmptyCheck {  
    public static void main(String[] args) {  
        // 示例1：null的Map  
        Map<String, String> nullMap = null;  
        System.out.println("Is nullMap null or empty? " + isNullOrEmpty(nullMap));  
  
        // 示例2：空的Map  
        Map<String, String> emptyMap = new HashMap<>();  
        System.out.println("Is emptyMap null or empty? " + isNullOrEmpty(emptyMap));  
  
        // 示例3：包含元素的Map  
        Map<String, String> nonEmptyMap = new HashMap<>();  
        nonEmptyMap.put("key1", "value1");  
        System.out.println("Is nonEmptyMap null or empty? " + isNullOrEmpty(nonEmptyMap));  
    }  
  
    /**  
     * 判断Map是否为null或者空  
     * @param map 要检查的Map  
     * @return 如果Map为null或者空，则返回true；否则返回false  
     */  
    public static boolean isNullOrEmpty(Map<?, ?> map) {  
        return map == null || map.isEmpty();  
    }  
}

Map<String, Integer> map = null;  
if (map == null) {  
    System.out.println("Map is null");  
} else {  
    System.out.println("Map is not null");  
}

Map<String, Integer> map = new HashMap<>();  
if (map.isEmpty()) {  
    System.out.println("Map is empty");  
} else {  
    System.out.println("Map is not empty");  
}

Map<String, Integer> map = new HashMap<>();  
if (map.size() == 0) {  
    System.out.println("Map is empty");  
} else {  
    System.out.println("Map is not empty");  
}

Map<String, Integer> map = getSomeMap(); // 假设这是从某个方法获取的Map  
if (map == null || map.isEmpty()) {  
    System.out.println("Map is null or empty");  
} else {  
    System.out.println("Map is not null and not empty");  
}

Map<String, Integer> map = getSomeMap(); // 假设这是从某个方法获取的Map  
if (Objects.isNull(map) || (Objects.nonNull(map) && map.isEmpty())) {  
    System.out.println("Map is null or empty");  
} else {  
    System.out.println("Map is not null and not empty");  
}  
// 注意：这个例子中Objects.nonNull(map)是多余的，因为如果map为null，第一个条件就会为真。  
// 这里只是为了展示Objects类的用法。

import java.util.HashMap;  
import java.util.Map;  
  
public class MapCheckExample {  
    public static void main(String[] args) {  
        // 示例1：null的Map  
        Map<String, Integer> nullMap = null;  
        checkMapStatus(nullMap);  
  
        // 示例2：空的Map  
        Map<String, Integer> emptyMap = new HashMap<>();  
        checkMapStatus(emptyMap);  
  
        // 示例3：非空的Map  
        Map<String, Integer> nonEmptyMap = new HashMap<>();  
        nonEmptyMap.put("one", 1);  
        nonEmptyMap.put("two", 2);  
        checkMapStatus(nonEmptyMap);  
    }  
  
    public static void checkMapStatus(Map<String, Integer> map) {  
        if (map == null) {  
            System.out.println("The map is null.");  
        } else if (map.isEmpty()) {  
            System.out.println("The map is empty.");  
        } else {  
            System.out.println("The map is not null and not empty. Size: " + map.size());  
        }  
    }  
}

import java.util.HashMap;  
import java.util.Map;  
  
public class SafeMapHandling {  
    public static void main(String[] args) {  
        Map<String, String> map = getMapFromSomewhere(); // 这个方法可能返回null  
        processMapSafely(map);  
    }  
  
    public static Map<String, String> getMapFromSomewhere() {  
        // 这个方法可能返回null或者一个Map实例，这里为了示例返回null  
        return null;  
    }  
  
    public static void processMapSafely(Map<String, String> map) {  
        if (map != null) {  
            // 安全地处理map，因为我们已经检查了它是否为null  
            if (map.isEmpty()) {  
                System.out.println("The map is empty, but not null.");  
            } else {  
                System.out.println("Processing non-empty map...");  
                // 在这里处理map中的元素...  
            }  
        } else {  
            System.out.println("The map is null, cannot process.");  
        }  
    }  
}