Java基础类(七):CollectionUtils工具类

x33g5p2x  于10个月前 转载在 Java  
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1、Pom包

从maven找到最新jar包如下:

<dependency>
        <groupId>org.apache.commons</groupId>
        <artifactId>commons-collections4</artifactId>
        <version>4.3</version>
    </dependency>

2、常用方法

2.1、集合判断

​ 判断集合是否为空:
     CollectionUtils.isEmpty(null): true
    CollectionUtils.isEmpty(new ArrayList()): true  
    CollectionUtils.isEmpty({a,b}): false

 判断集合是否不为空:
    CollectionUtils.isNotEmpty(null): false
    CollectionUtils.isNotEmpty(new ArrayList()): false
    CollectionUtils.isNotEmpty({a,b}): true

源码分析

public class CollectionUtils {
    public static boolean isEmpty(Collection<?> coll) {
        return coll == null || coll.isEmpty();
    }
    public boolean isEmpty() {
        return size == 0;
    }
}

2.2、并集

public class TestCollectionUtils {

    public static void main(String[] args) {
        String[] arrayA = new String[] { "A", "B", "C", "D", "E", "F" };
        String[] arrayB = new String[] { "B", "D", "F", "G", "H", "K" };
        List<String> listA = Arrays.asList(arrayA);
        List<String> listB = Arrays.asList(arrayB);
        //2个数组取并集
        System.out.println(ArrayUtils.toString(CollectionUtils.union(listA, listB)));
        //[A, B, C, D, E, F, G, H, K]
    }

}

2.3、交集

public class TestCollectionUtils {

    public static void main(String[] args) {
        String[] arrayA = new String[] { "A", "B", "C", "D", "E", "F" };
        String[] arrayB = new String[] { "B", "D", "F", "G", "H", "K" };
        List<String> listA = Arrays.asList(arrayA);
        List<String> listB = Arrays.asList(arrayB);
        //2个数组取交集
        System.out.println(ArrayUtils.toString(CollectionUtils.intersection(listA, listB)));
        //[B, D, F]
    }

}

2.4、交集的补集(析取)

public class TestCollectionUtils {

    public static void main(String[] args) {
        String[] arrayA = new String[] { "A", "B", "C", "D", "E", "F" };
        String[] arrayB = new String[] { "B", "D", "F", "G", "H", "K" };
        List<String> listA = Arrays.asList(arrayA);
        List<String> listB = Arrays.asList(arrayB);
        //2个数组取交集 的补集
        System.out.println(ArrayUtils.toString(CollectionUtils.disjunction(listA, listB)));
        //[A, C, E, G, H, K]
    }

}

2.5、差集

public class TestCollectionUtils {

    public static void main(String[] args) {
        String[] arrayA = new String[] { "A", "B", "C", "D", "E", "F" };
        String[] arrayB = new String[] { "B", "D", "F", "G", "H", "K" };
        List<String> listA = Arrays.asList(arrayA);
        List<String> listB = Arrays.asList(arrayB);
        //arrayA扣除arrayB
        System.out.println(ArrayUtils.toString(CollectionUtils.subtract(listA, listB)));
        //[A, C, E]   
    }

}

2.6、不可修改的集合【已经过期】

public class TestCollectionUtils {

    public static void main(String[] args) {
        Collection<String> c = new ArrayList<>();
        //deprecated
        Collection<String> s = CollectionUtils.unmodifiableCollection(c);
        c.add("a");
        c.add("b");
        c.add("c");
        //Exception in thread "main" java.lang.UnsupportedOperationException
        //s.add("have a error");
        System.out.println(s);
    }

}

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