英文:
Java how to call method in another class
问题
抱歉,以下是您要翻译的内容:
抱歉,这个问题比较基础,但我正在学习,刚开始学编程。我尝试调用另一个类中的方法,但是如果不传递给“Cypher”类构造函数所需的值,我就无法调用它。每次我在“Menu”类中使用“Cypher”类的方法并且想要调用“Cypher”类的方法时,我真的需要一个新的“Cypher”类实例吗?或者我该如何重写以避免下面的情况。
public class Runner {
private static Cypher c;
public static void main(String[] args) {
Menu m = new Menu();
m.displayMenu();
//c=new Cypher(3,2);// 除非我添加这一行,否则无法工作
c.displayCypher("text");
}
}
public class Cypher {
private int keyTotalRows;
private int keyStartRow;
public Cypher(int key, int offset) throws Exception {
}
public void displayCypher(String text) {
System.out.println("Plain text:" + text);
System.out.println("Key: Number of Rows:" + keyTotalRows + "\n" + "Key Start Row: " + keyStartRow);
}
}
public class Menu {
private Scanner s;
private void enterKey() {
s = new Scanner(System.in);
System.out.println("Enter key >");
int key = Integer.parseInt(s.next());
System.out.println("Enter offset >");
int offset = Integer.parseInt(s.next());
System.out.println(" Key:" + key + "\n" + " Offset:" + offset);
}
public static void displayMenu() {
System.out.println("Menu");
}
}
英文:
Sorry for the basic question but I'm learning, new to programming. I am trying to call a method that is in another class but I'm unable to without passing in the required values for the constructor of Cypher
class. Do i really need a new instance of Cypher
class each time i use a method in the Menu
class and want to call a method of the Cypher
class or how do I rewrite to avoid below.
public class Runner {
private static Cypher c;
public static void main(String[] args) {
Menu m = new Menu();
m.displayMenu();
//c=new Cypher(3,2);// wont work unless i add this line
c.displayCypher("text");
}
}
public class Cypher {
private int keyTotalRows;
private int keyStartRow;
public Cypher(int key, int offset) throws Exception {
}
public void displayCypher(String text) {
System.out.println("Plain text:" + text);
System.out.println("Key: Number of Rows:" + keyTotalRows + "\n" + "Key Start Row: " + keyStartRow);
}
}
public class Menu {
private Scanner s;
private void enterKey() {
s = new Scanner(System.in);
System.out.println("Enter key >");
int key = Integer.parseInt(s.next());
System.out.println("Enter offset >");
int offset = Integer.parseInt(s.next());
System.out.println(" Key:" + key + "\n" + " Offset:" + offset);
}
public static void displayMenu() {
System.out.println("Menu");
}
答案1
得分: 2
Few things:. Your methods are private which means you cannot call them outside the class.
change that and you will be able to create your object and call them.
Menu menu = new Menu();
menu.otherMethod();
However as the method calls c which is null you will get a null exception.
You should test for it and then call object c inner methods
if (this.c != null)
{c.displayOtherCypherType(""); }
else
{//do something here}
In order to be able to send Cypher from outside the class use a constructor that receives a Cypher object and assigns it to c or have a public set method that receives it and assigns it
public setCypher(Cypher cypher)
{
(this.c = cypher);
}
Now If you want to call Cypher methods without instantiating it you can create a static method inside it and call that method.
note that it too should be public or you won't be able to call it
英文:
Few things:. Your methods are private which means you cannot call them outside the class.
change that and you will be able to create your object and call them.
Menu menu=new Menu() ;
menu.otherMethod();
However as the method calls c which is null you will get a null exception.
You should test for it and then call object c inner methods
If (this.c! =null)
{c.displayOtherCypherType("" ) ;}
else
{//do something here}
In order to be able to send Cypher from outside the class use a constructor that receives a Cypher object and assigns it to c or have a public set method that receives it and assigns it
public setCypher(Cypher cypher)
{
(this.c=cypher) ;
}
Now If you want to call Cypher methods without instantiating it you can create a static method inside it and call Tha method.
note that it to should be public or you won't be able to call it
答案2
得分: 1
你在这里声明了一个Cypher类型的静态变量 c
。所以在没有对象声明的情况下,你不能使用 c
变量访问Cypher类的方法。但是你可以从任何类中调用 c
变量,因为它是一个静态变量。但是你的Cypher类没有任何静态方法,所以你不能在没有对象初始化的情况下调用这些方法。
所以你必须声明一个静态方法或者需要创建一个对象来访问Cypher类的方法。
但是如果你声明了一个带初始化的Cypher类型静态变量,那么你可以从任何类中调用 c
,并且还可以使用 c
变量引用调用Cypher类的方法,就像这样:
// 在Runner类中声明这个
public static Cypher c = new Cypher();
// 然后在任何类中调用
Runner.c.yourMethod();
祝编码愉快。
英文:
You declare a Cypher type static variable c
here. so you can't access the Cypher class method using c
variable without object declaration. But you can call the c
variable from any class because it's a static variable. But your Cypher class don't have any static Method so you can't call these methods without object initialization.
So you must declare a static method or need to create an object for the access method from Cypher class.
But if you declare Cypher type static variable with initialization. then you can call c from any class and also called Chyper class method using the c
variable reference. like:
// Declare this on Runner class
public static Cypher c = new Cypher();
// And then call from any class like
Runner.c.yourMethod();
Happy Coding.
答案3
得分: 0
如果你不想创建一个实例,你可以将方法设为静态的。
像这样:
public static void displayCypher(String text) {
System.out.println("明文:" + text);
System.out.println("密钥:总行数:" + keyTotalRows + "\n" + "密钥起始行:" + keyStartRow);
}
然后你可以在另一个类中调用这个函数:
Cypher.displayCypher();
英文:
If you don't want to create an instance, you can make the method static.
Something like this:
public static void displayCypher(String text) {
System.out.println("Plain text:" + text);
System.out.println("Key: Number of Rows:" + keyTotalRows + "\n" + "Key Start Row: " + keyStartRow);
}
Then you can call this function in another class like
Cypher.displayCypher()
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