为什么我的序列号系统重复数字001 ?

Question

我试图在Java中为我的联系人列表分配一个唯一的ID。除了第一个数字之外，一切正常。在移动到ID002之前，它总是重复ID001两次。知道为什么吗?

private static String getSN() {
    String SN = "ID001";
    for (int i = 0; i < AddressBook.size(); i++) {
        if(AddressBook.size()<10){
        if (AddressBook.get(i).substring(0, 4).contains("ID00"+i));
        int snString = i+1;
        SN = "ID00"+Integer.toString(snString);
        if(SN.equals("ID0010")){
            SN = ("ID010");
        }
        }
        else{
            if(AddressBook.size()<100){
                if (AddressBook.get(i).substring(0, 5).equals("ID0"+i));
                int snString = i+1;
                SN = "ID0"+Integer.toString(snString);
                if(SN.equals("ID00100")){
                    SN = ("ID0100");
                }
                }
        }
    }
    return SN;
}

Answer 1

为什么我的序列号系统重复数字001?

因为SN是一个局部变量。静态方法中的局部变量仍然是局部变量，每次调用该方法返回时，它都会消失。

你可能应该使用static字段…

Answer 2

我想出了一个更简单的方法。每次我向联系人列表中添加一个新成员时，我都会添加一个序列号，而不是使用循环。

private static void setSN() {
    if (AddressBook.size() < 10) {
        for (int i = 0; i < AddressBook.size(); i++) {
            String tempString = AddressBook.get(i);
            if (tempString.contains("ID00" + Integer.toString(AddressBook.size() + 1))) {
                SN = "ID00" + Integer.toString(AddressBook.size() + 2);
            }
            else{
                SN = "ID00" + Integer.toString(AddressBook.size() + 1);
        }
        }
    } 
    else {
        if (AddressBook.size() < 100) {
            for (int i = 0; i < AddressBook.size(); i++) {
                String tempString = AddressBook.get(i);
                if (tempString.contains("ID0" + Integer.toString(AddressBook.size() + 1))) {
                    SN = "ID0" + Integer.toString(AddressBook.size() + 2);
                }
                else{
                    SN = "ID0" + Integer.toString(AddressBook.size() + 1);
            }

        }
        }
    }
}

Answer 3

试试这个:
1. 修改AddressBook.get(i).substring(0, 4).contains("ID00"+i)
AddressBook.get(i).substring(0, 5).contains("ID00"+(i+1))
2. 修改int snString = i+1; by
int snString = i+2;
3.这是因为列表的索引从0开始。

private static String getSN() {
    String SN = "ID001";
    for (int i = 0; i < AddressBook.size(); i++) {
        if(AddressBook.size()<10){
            if (AddressBook.get(i).substring(0, 5).contains("ID00"+(i+1))){
                int snString = i+2;
                SN = "ID00"+Integer.toString(snString);
            }
            if(SN.equals("ID0010")){
                SN = ("ID010");
            }
        } else {
            if(AddressBook.size()<100){
                if (AddressBook.get(i).substring(0, 5).equals("ID0"+(i+1))) {
                    int snString = i+2;
                    SN = "ID0"+Integer.toString(snString);
                }
                if(SN.equals("ID00100")){
                    SN = ("ID0100");
                }
            }
        }
    }
    return SN;
}