public class Test {  
    public List left(Integer[] a,Integer[] b){//c1是相对大的集合，C2是小集合
        List<Integer> c1 = new ArrayList<Integer>(),
                      c2= new ArrayList<Integer>(),
                      list = new ArrayList<Integer>();
        c1.addAll(Arrays.asList(a));
        c2.addAll(Arrays.asList(b));
        for(int i=0;i<c1.size();i++){
            if(!c2.contains(c1.get(i))){
                list.add(c1.get(i));
            }
        }        
        return list;
    }
    
    public static void main(String[] args) {
        Integer[] c ={1,2,3,4,56,6};
        Integer[] d = {2,3,4};
        
        
        List list = new Test().left(c, d);
        for(Object o:list){
            System.out.println((Integer)o);
        }
    }  
}