How to Use Variables Declared in Another Class

How Do I Access One Variable From Another Class?

  • If the field myNum is declared as public, you can access it by
    any other class by typing the name of the object instance.myNu

  • If the filed myNum is declared as public static, you can access it
    from any other class by typing the name of the class.myNum

  • If the field myNum is private, you need getters and setters, namely,
    methods to access the file from an instance of the class that
    contains it. Google them to get up to speed on why they're useful and
    why you should use them.



ClassOne instance = new ClassOne();

ClassTwo instante2 = new ClassTwo();

instance2.myNewInt = instance.myNum;

//public static

ClassTwo instante2 = new ClassTwo();

instance2.myNewInt = ClassOne.myNum;


ClassOne instance = new ClassOne();

ClassTwo instante2 = new ClassTwo();

instance2.myNewInt = instance.getMyNum();

//and inside of ClassOne you'll have

private int MyNum = 5;

public getMyNum(){

return MyNum;



If the variable was only declared locally (inside the body of one of ClassOne's methods), you're gonna need to assign it to a filed, so that you can later access it from other classes.

Reading Material:

Getters and Setters

Access modifiers

How do I access variables from another class in Java?

If you simply want to access the value of a property from outside of the class, then you need to create getters for each one of the properties you want to retrieve.

If you want to modify these values from outside of the class, you need to create a setter.

Getters and Setters are simply methods that allow you to access properties of a class outside of it.

If you have the class Customer and want to access and change it's name from outside, you'd create 2 methods,

//declare the property
private String name;

public String getName(){

public void setName(String newName){ = newName;

//You can then instantiate a Customer object anywhere else and have access to those //properties

Customer cust = new Customer();
System.out.println("Oh hi " + cust.getName());
//output "Oh hi Mark"

Read more on getters and setters

Also, best practices tip: instance variables should always be declared as private to help encapsulation. If no access modifier is provided for an instance variable in Java, it defaults to the default modifier, which makes the variable accessible for every class within the same package.


Your specific error is that you are creating a new Customer object within your customerDetails method, and you're not returning this Customer object. Therefore, as soon as the method has been executed, the Customer object you created inside is destroyed (cleared from memory,Garbage collected), because there is no further reference to it.

You either need to

Method 1: Change the return type of your customerDetails method from void to Customer and add a return a statement at the end, then you would simply need to instantiate a Customer object from your booking class, like so

public Customer customerDetails(){               
Customer a = new Customer();
//your logic to set all of the properties
return a;

in your booking class

Customer myCust = new Customer();
myCust = myCust.customerDetails();

I would not prefer this method, because as you see, you're just creating an empty object then reassigning to it. You may alternatively add the static keyword after public so that you can call it without having instantiated an object of the class, like so

booking class

Customer myCust = Customer.customerDetails();

Method 2: remove the Customer a = new Customer() from the customerDetails altogether and simply use = sc.nextLine() to set the name of whatever instance is calling this method.

Then on bookings class, instantiate a new Customer object and call the method.

Customer myCust = new Customer();

how to use variable which is declare in another class


1.Use static variable:

Declare static String collect;
and access it from other class as <YourClassNmae>.collect;
where YourClassName is the class in which you have declared the static variable.

2.Use Application class

Create application class extending Application

public class MyApplication extends Application {

private String someVariable;

public String getSomeVariable() {
return someVariable;

public void setSomeVariable(String someVariable) {
this.someVariable = someVariable;

Declare the application class name in manifest like:


Then in your activities you can get and set the variable like so:

// set
((MyApplication) this.getApplication()).setSomeVariable(collect);

// get
String collect = ((MyApplication) this.getApplication()).getSomeVariable();

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