Question

I have this code that reads from XML file. It gets five strings (groupId, groupType, filePath, author, and lineNo), and it first saves them in a String Array. Then, the String Array is saved in an ArrayList. Finally, the last “for” displays the content of the ArrayList.

The problem that when I want to display the content, I get just the last added string array. The following is the code and the output. Can anyone figure out what is the problem?

ArrayList<String[]> developerTypes = new ArrayList<String[]>();
String[] developerInfo = {null, null, null, null, null};
String[] developerInfoR = {null, null, null, null, null};

String groupId;
String groupType;
String filePath;
String author;
String lineNo;


SAXBuilder builder = new SAXBuilder();
Document doc = (Document) builder.build("A.xml");
Element clones = doc.getRootElement();

// Loop of clones' children (clone_group)
List<Element> parentElements = clones.getChildren();
for(Element parentElement:parentElements){


    // Loop of clone_group's children (clone_fragment)
    List<Element> elements = parentElement.getChildren();
    for(Element element:elements){

        // Loop of clone_fragment's children (blameInfo)
        List<Element> childelements = element.getChildren();
        for(Element childElement:childelements){

            groupId = parentElement.getAttributeValue("groupid");
            groupType = parentElement.getAttributeValue("type");
            filePath = element.getAttributeValue("file");
            author = childElement.getAttributeValue("author");
            lineNo = childElement.getAttributeValue("lineNo");
            //System.out.print(groupId + " - ");
            //System.out.print(groupType + " - ");
            //System.out.print(file + " - ");
            //System.out.println(author);
            developerInfo[0] = groupId;
            developerInfo[1] = groupType;
            developerInfo[2] = filePath.substring(1, filePath.lastIndexOf("."));;
            developerInfo[3] = author;
            developerInfo[4] = lineNo;
            developerTypes.add(developerInfo);

        }// for (blameInfo)    
    }// for (clone_fragment)
}// for (clone_group)

// Display the content of the Arraylist    
for(int i = 0; i< developerTypes.size(); ++i){

    developerInfoR = developerTypes.get(i);

    for(int j = 0; j< developerInfoR.length; ++j){

        System.out.print(developerInfoR[j] + " ");

    }
    System.out.print("\n");

}

The Output:

309 Type-3 builtin/update-index.c Jonathan Nieder 704 
309 Type-3 builtin/update-index.c Jonathan Nieder 704 
309 Type-3 builtin/update-index.c Jonathan Nieder 704 
309 Type-3 builtin/update-index.c Jonathan Nieder 704 
309 Type-3 builtin/update-index.c Jonathan Nieder 704 
309 Type-3 builtin/update-index.c Jonathan Nieder 704 
309 Type-3 builtin/update-index.c Jonathan Nieder 704 
309 Type-3 builtin/update-index.c Jonathan Nieder 704 
309 Type-3 builtin/update-index.c Jonathan Nieder 704 
309 Type-3 builtin/update-index.c Jonathan Nieder 704 
309 Type-3 builtin/update-index.c Jonathan Nieder 704 
309 Type-3 builtin/update-index.c Jonathan Nieder 704 
...

Answer 1

The problem that when I want to display the content, I get just the last added string array.

No, you find that you’ve got many references to the same string array… because that’s what you’ve added. You’ve only got one string array object; developerInfo is just a reference to that array. When you call developerTypes.add(developerInfo) that’s copying the reference into the ArrayList, so you’ve got the same reference lots of times.

You should pull the declaration and instantiation of developerInfo into the loop:

String[] developerInfo = {
    groupId,
    groupType,
    filePath.substring(1, filePath.lastIndexOf(".")),
    author,
    lineNo
};
developerTypes.add(developerInfo);

Likewise your code would be cleaner if you didn’t declare developerInfoR until you used it:

for(int i = 0; i< developerTypes.size(); ++i){
    String[] developerInfoR = developerTypes.get(i);
    for(int j = 0; j< developerInfoR.length; ++j){
        System.out.print(developerInfoR[j] + " ");
    }
    System.out.print("\n");
}

Or even better, use the enhanced for loop:

for (String[] developerInfoR : developerTypes) {
    for (String info : developerInfoR) {
        System.out.print(info + " ");
    }
    System.out.print("\n");
}

In general, you should declare local variables with the smallest scope you can get away with, as late as possible, ideally assigning a value at the point of declaration. Declaring all the variables at the top of the method really hurts readability.