Java中两个List的比较，并使用JSTL在JSP中以表格格式显示两个List之间的差异

Question

I have two Arraylist namely-

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

I have two methods which returns the defined ArrayList values individually. the first arraylist ie one has more values as compared to second arraylist ie two.

Now I want to

compare the values of both the array list and find out there difference

and display that in tabular format.Moreover as the fi rst Arraylsit one has more values as compared to two .So when there is only values of one arraylsit 0 should be displayed as there difference.

EDIT-1

I tried to achieve calculate difference as-

  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; } 

The output I receive is- But It does not give correct difference.Whats the mistake I have done.?

Answer 1

If i have understood your question correctly. What you want to do is print the difference if both the array list has values for same index or print zero when only one array list has value for the same index.

for this there are two possibilities.

If your array list only contains non-zero value. You could change the condition of for loop as follows

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

Then change the comparing function as follows:

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;
 }

If your arraylist contains zero values. I would suggest doing something like this

  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

This may solve that problem. But I haven't tried it yet on an object using a self-written class.

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

I don't know if your algorithm in doing the comparison is right. For example if x1 = -1 and 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);
}