一:CollectionUtils
例1: 判断集合是否为空: CollectionUtils.isEmpty(null): true CollectionUtils.isEmpty(new ArrayList()): true CollectionUtils.isEmpty({a,b}): false 例2: 判断集合是否不为空: CollectionUtils.isNotEmpty(null): false CollectionUtils.isNotEmpty(new ArrayList()): false CollectionUtils.isNotEmpty({a,b}): true 例3:2个集合间的操作: 集合a: {1,2,3,3,4,5} 集合b: {3,4,4,5,6,7} CollectionUtils.union(a, b)(并集): {1,2,3,3,4,4,5,6,7} CollectionUtils.intersection(a, b)(交集): {3,4,5} CollectionUtils.disjunction(a, b)(交集的补集): {1,2,3,4,6,7} CollectionUtils.disjunction(b, a)(交集的补集): {1,2,3,4,6,7} CollectionUtils.subtract(a, b)(A与B的差): {1,2,3} CollectionUtils.subtract(b, a)(B与A的差): {4,6,7}
二: