为什么我的方法返回空密码？
我有两个类：生成器类和系统管理类。 Generator 类，我可以生成密码。 SystemManagement 类导入 Generator（从另一个包）并包含附加信息。
当我创建一个 SystemManagement 对象并对其调用 getPassword() 时，我返回 null。为什么会发生这种情况？
生成器：
public class Generator {
private static String password;
private static Generator instance;
public String nextPassword() {
char[] allowedCharacters = {'a', 'b', 'c', 'd', 'e', 'f', '1', '2', '3', '4', '5','6'};
SecureRandom random = new SecureRandom();
StringBuffer password1 = new StringBuffer();
for (int i = 0; i < password1.length(); i++) {
password1.append(allowedCharacters[random.nextInt(allowedCharacters.length)]);
}
password = password1.toString();
return password;
}
public String currentPassword() {
return password;
}
public static void setPassword(String password) {
Generator.password = password;
}
public static Generator getInstance() {
if (instance == null) {
instance = new Generator();
}
return instance;
}
}
系统管理：
public class SystemManagement implements Serializable {
private String name;
private String family;
private String password;
public SystemManagement() {
}
public SystemManagement(String password) {
this.password = Generator.getInstance().nextPassword();
}
public Students addStudent(String name, String family) {
Students student = new Students(name, family);
students.add(student);
return student;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
}
I have two classes: a Generator class and a SystemManagement class. The Generator class, I can generate a password. The SystemManagement class imports Generator (from another package) and includes additional information.
When I make a SystemManagement object and call getPassword() on it, I get back null. Why is this happening?
Generator:
public class Generator {
private static String password;
private static Generator instance;
public String nextPassword() {
char[] allowedCharacters = {'a', 'b', 'c', 'd', 'e', 'f', '1', '2', '3', '4', '5','6'};
SecureRandom random = new SecureRandom();
StringBuffer password1 = new StringBuffer();
for (int i = 0; i < password1.length(); i++) {
password1.append(allowedCharacters[random.nextInt(allowedCharacters.length)]);
}
password = password1.toString();
return password;
}
public String currentPassword() {
return password;
}
public static void setPassword(String password) {
Generator.password = password;
}
public static Generator getInstance() {
if (instance == null) {
instance = new Generator();
}
return instance;
}
}
SystemManagement:
public class SystemManagement implements Serializable {
private String name;
private String family;
private String password;
public SystemManagement() {
}
public SystemManagement(String password) {
this.password = Generator.getInstance().nextPassword();
}
public Students addStudent(String name, String family) {
Students student = new Students(name, family);
students.add(student);
return student;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
}
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评论（5）
我可以发现您的代码存在几个问题：
您的
nextPassword()方法始终返回一个空的String作为密码，因为您迭代了一个空的StringBuilder长度为 0。当您使用无参数构造函数创建新的
SystemManagement对象时，您的密码为 null，因为您没有为其分配任何内容 (除非您使用setPasswordsetter）。当您使用采用
String的构造函数创建新的SystemManagement对象时，您会忽略该参数，并且您的password为空，因为 < code>nextPassword() 始终返回空String。I can spot a couple of problems with your code:
Your
nextPassword()method always returns an emptyStringas the password because you iterate over an emptyStringBuilderwith length 0.When you create a new
SystemManagementobject with the parameter-less constructor, yourpasswordis null because you assign nothing to it (unless you use thesetPasswordsetter).When you create a new
SystemManagementobject with the constructor that takes aString, you ignore the parameter and yourpasswordis empty becausenextPassword()always returns an emptyString.password1.length() 第一次是 0，所以它永远不会被填充？
password1.length() is 0 first time, so it never gets filled?
我想字符串缓冲区的长度是
0。I would imagine that that would be
0for thelengthof the string buffer.如果您调用不带参数的构造函数（例如
sys = new SystemManagement();），则永远不会设置新对象的password成员。仅当您调用采用String的构造函数时才会发生这种情况（您会忽略该构造函数）。If you call the constructor with no arguments (like
sys = new SystemManagement();), the new object'spasswordmember is never set. That only happens if you call the constructor that takes aString—which you ignore.for 循环永远不会运行，因为此时
password1.length()将为 0。The for loop will never run as
password1.length()will be 0 at this time.