比较Java中的两个List，并使用JSTL在JSP中以表格格式显示两个List之间的差异

Question

我有两个Arraylist即 -

    List<java_test> one=new ArrayList<java_test>();
    List<java_test> two=new ArrayList<java_test>();

我有两个方法，它们分别返回定义的ArrayList值。 第一个arraylist，即一个与第二个arraylist相比有更多的值，即两个。

现在我想

  

比较两个数组列表的值并找出它们   差

并以表格格式显示。此外，因为fi 第一个Arraylsit 与相比具有更多值。当只有一个arraylsit的值 0 ，因为存在差异。

修改-1

我试图将计算差异作为 -

＆＃13;

＆＃13;

 public LinkedHashMap < String, List < Double >> diff() {
   for (int i = 0; i < one.size() && i < two.size(); i++) {
     Comaprision refObj = one.get(i);
     Comaprision stObj = two.get(i);
     Double x = refObj.getBeam_current();
     Double y = stObj.getBeam_current();


     x = refObj.getBeam_energy();
     y = stObj.getBeam_energy();
     comparing(x, y);

     x = refObj.getSt2_vs2_bag1_rb();
     y = stObj.getSt2_vs2_bag1_rb();
     comparing(x, y);

     x = refObj.getSt2_vs2_bag2_rb();
     y = stObj.getSt2_vs2_bag2_rb();
     comparing(x, y);

     x = refObj.getSt2_vs2_bag3_rb();
     y = stObj.getSt2_vs2_bag3_rb();
     comparing(x, y);

     x = refObj.getSt2_vs2_bag4_rb();
     y = stObj.getSt2_vs2_bag4_rb();
     comparing(x, y);


     dif.put("", z);


   }
   return dif;
 }

 public List < Double > comparing(Double x1, Double y1) {

   if ((x1 > y1)) {

     z.add(x1 - y1);
     System.out.println("value of z is" + z);
   } else {
     z.add(y1 - x1);

   }


   return z;
 }

＆＃13;

＆＃13;

＆＃13;

我收到的输出是 - 但它没有给出正确的区别。我所犯的错误是什么。？

Answer 1

如果我正确理解了你的问题。如果数组列表具有相同索引的值，或者当只有一个数组列表具有相同索引的值时打印零，则要打印差异。

为此有两种可能性。

如果您的数组列表仅包含非零值。您可以按如下方式更改for循环的条件

for (int i = 0; i < one.size(); i++) // since you have already specified first array list is larger than the second.

然后按如下方式更改比较功能：

public List < Double > comparing(Double x1, Double y1) {

 if(y1 == 0)
 {
    z.add(0);
 }
 else
 if ((x1 > y1)) {

 z.add(x1 - y1);
 System.out.println("value of z is" + z);
 } else {
 z.add(y1 - x1);

 }


 return z;
 }

如果你的arraylist包含零值。我建议做这样的事情

 public LinkedHashMap < String, List < Double >> diff() {
   for (int i = 0; i < one.size(); i++) {
     if(i < two.size()){
     Comaprision refObj = one.get(i);
     Comaprision stObj = two.get(i);
     Double x = refObj.getBeam_current();
     Double y = stObj.getBeam_current();


     x = refObj.getBeam_energy();
     y = stObj.getBeam_energy();
     comparing(x, y);

     x = refObj.getSt2_vs2_bag1_rb();
     y = stObj.getSt2_vs2_bag1_rb();
     comparing(x, y);

     x = refObj.getSt2_vs2_bag2_rb();
     y = stObj.getSt2_vs2_bag2_rb();
     comparing(x, y);

     x = refObj.getSt2_vs2_bag3_rb();
     y = stObj.getSt2_vs2_bag3_rb();
     comparing(x, y);

     x = refObj.getSt2_vs2_bag4_rb();
     y = stObj.getSt2_vs2_bag4_rb();
     comparing(x, y);


     
     }
     else{
        for(i=0; i<(the number of variables your comparing in the if condition above); i++)
        {
        z.add(0.0);
        }
     }
   }
   dif.put("", z);
   return dif;
 }

 public void comparing(Double x1, Double y1) {

   if ((x1 > y1)) {

     z.add(x1 - y1);
     System.out.println("value of z is" + z);
   } else {
     z.add(y1 - x1);

   }
 }

Answer 2

这可以解决这个问题。但我还没有尝试过使用自编类的对象。

public static void main(String[] args) {
    // TODO Auto-generated method stub

    List<String> list1 = new ArrayList<String>();
    List<String> list2 = new ArrayList<String>();


    /*Put values to both lists*/
    list1.add("John");
    list1.add("Doe");

    list2.add("John");
    list2.add("Doe");

    /*Add other objects to list2. This will be the differences*/
    list2.add("Jane");
    list2.add("Roe");


    System.out.println("Printing two lists before retaining differences");
    System.out.println("list1: "+list1);
    System.out.println("list2: "+list2+"\n");

    System.out.println("Similarities removed. Differences stored to list2");
    list2.removeAll(list1);
    System.out.println("differences: "+list2);
}

}

Answer 3

我不知道你的算法在进行比较时是否正确。例如，如果x1 = -1且x2 = 5：x2 - x1 = 5 - (-1) = 5 + 1 = 6

public static void main(String[] args) {
    // TODO Auto-generated method stub

    List<Double> list1 = new ArrayList<Double>();
    List<Double> list2 = new ArrayList<Double>();
    List<Double> result = new ArrayList<Double>(); //where result will be stored

    //Load with values
    list1.addAll(Arrays.asList(new Double[]{3.0,-5.0,7.0,-9.0,11.0,-13.0}));
    list2.addAll(Arrays.asList(new Double[]{1.0,1.0,1.0,1.0,1.0,1.0}));
    System.out.println("list1: "+list1);
    System.out.println("list2: "+list2);

    for(int i=0; i<list1.size() && i<list2.size(); i++) {
        double d1 = list1.get(i);
        double d2 = list2.get(i);

        //If d1 is greater than d2, do d1 minus d2 otherwise do d2 minus d1
        //I don't know if that is really the purpose of doing the difference in your code
        //Store result to result list
        result.add( d1>d2 ? d1-d2 : d2-d1);

    }

    //Print the result
    System.out.println("result: "+result);
}