Question

public class Human {
private int age;
private float height;
private float weight;
private String name = new String();

public Human() {
}

public Human(String name, int age, float height, float weight) {
    this.name = name;
    this.age = age;
    this.height = height;
    this.weight = weight;
}

public Human(Human human) {
    this.name = human.getName();
    this.age = human.getAge();
    this.height = human.getHeight();
    this.weight = human.getWeight();
}

public static void writeFile(Human human, OutputStream output) throws IOException {
    output.write((human.getName() + "\n").getBytes());
    output.write((human.getAge() + "\n").getBytes());
    output.write((human.getHeight() + "\n").getBytes());
    output.write((human.getWeight() + "\n").getBytes());
}

public static Human readFile(InputStream input) throws IOException {
    int temp;
    String file = "";
    String[] fileArray;

    file += (char) input.read();
    while ((temp = input.read()) != -1) {
        file += (char) temp;
    }

    fileArray = file.split("\n", 0);

    Human madeHuman = new Human(fileArray[0], Integer.parseInt(fileArray[1]), Float.parseFloat(fileArray[2]), Float.parseFloat(fileArray[3]));

    return madeHuman;
}

public static void writeArrayListInFile(ArrayList<Human> humans, OutputStream output) throws IOException {
    for (int i = 0; i < humans.size(); i++) {
        output.write((humans.get(i).getName() + "\n").getBytes());
        output.write((humans.get(i).getAge() + "\n").getBytes());
        output.write((humans.get(i).getHeight() + "\n").getBytes());
        output.write((humans.get(i).getWeight() + "\n").getBytes());
        output.write('#');
    }
}

public static ArrayList<Human> readArrayListFromFile(InputStream input) throws IOException {
    int temp = ' ';
    String file = "";
    String[] fileArray1;
    String[][] fileArray2 = new String[10][];
    ArrayList<Human> madeHumanArrayList = new ArrayList<Human>();

    file += (char) input.read();
    while ((temp = input.read()) != -1) {
        file += (char) temp;
    }

    fileArray1 = file.split("#", 0);

    for (int i = 0; i < fileArray1.length; i++)
        for (int j = 0; j < 4; j++)
            fileArray2[i] = fileArray1[i].split("\n", 0);

    for (int i = 0; i < fileArray2.length; i++)
        madeHumanArrayList.add(new Human(fileArray2[i][0], Integer.parseInt(fileArray2[i][1]), Float.parseFloat(fileArray2[i][2]), Float.parseFloat(fileArray2[i][3])));//null pointer exception

    return madeHumanArrayList;
}

}

虽然我已经初始化了我的arraylist，但它给了我nullpointer异常。我是java中的一个重要人物，所以我会感激任何简单的帮助。

Answer 1

当我将对象添加到arraylist
时，我已将评论放在最后一行

你的代码是

for (int i = 0; i < fileArray1.length; i++)
    for (int j = 0; j < 4; j++)
        fileArray2[i] = fileArray1[i].split("\n", 0);

这意味着您只需将fileArray2中的值设置为fileArray1.length

的索引

但是你在这个数组中读取值

for (int i = 0; i < fileArray2.length; i++)

因此，除非fileArray1.length == fileArray2.length您将阅读未初始化的值。

我建议你丢弃第二个数组，因为它没有做任何有用的事情并合并两个外部循环，然后你会尝试读取你没写的东西。

for (String humanStr : file.split("#", 0)) {
    String[] h = humanStr.split("\n", 0);

    madeHumanArrayList.add(new Human(h[0], Integer.parseInt(h[1]), 
                                     Float.parseFloat(h[2]), Float.parseFloat(h[3])));
}

最后，除非有充分理由，否则我不会使用float。我建议使用double或BigDecimal，因为这些更精确。

java arraylist添加空指针异常

1 个答案: