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Dart Classes

Class Anatomy

Next picture show you the features of a Class. As you can see a Class has a name, properties and methods. In this picture we show you an example of a class called: Account with two properties act_number, act_type and 4 methods.

Class Anatomy

Pattern:

Next syntax pattern is the most common. A class is by default derived from Object class, you do not have to specify this in class definition. A class can have a constructor that has the same name as the class. Class name start with uppercase so the constructor start also with uppercase.

//define a class
class ClassName {
    //definition of fields (attributes/properties)
    type this.field1;
    ...
    //define eventual setters+getters
    ...
    // define constructor (having same name as the class)
    ClassName(type param1, type param2, ...) {
        this.field1 = param1;
        ...
    }
    // define other functions,
    type functionName(params) {
        ...
    }
}

Practice Example

Next example is here for you to jump ahead into study. The same example is available in Java tutorial. If you are a java developer, you can open:java class in a new window and compare the two examples. If you do not know Java you can just study the example below:

Implement Class

/* define a class */
class Account {
    // class public properties
    int act_number;
    String act_type;
    // class internal field
    int _act_amount = 0;
    //class constructor (same name ass class)
    Account(int p_number, String p_type) {
        this.act_number = p_number;
        this.act_type = p_type;
    }
    //fists class methods
    int withdraw(int p_amount) {
        int result;
        if (_act_amount > p_amount) {
           this._act_amount -= p_amount;
           result = p_amount;
        } else {
           result = p_amount = this._act_amount;
           this._act_amount = 0;
           return result;
        }
    }
    //second method
    void deposit(int p_amount) {
        this._act_amount += p_amount;
    }
    //third method
    int closure() {
        int result = this._act_amount;
        this._act_amount = 0;
        return result;
    }
    //supplementary method
    int get amount {
        return this._act_amount;
    }
} //end of class

Notes:

• Dart do not have "public/private" access modifiers like Java;
• Private fields start with underscore. _act_amount is private;
• Dart do not have Long type, so I have used int type instead;
• In dart, getters do not have parameter list and start with "get" keyword;

Test Account

void main() {
    //create an instance of Account
    Account myCheckAccount = new Account(2021,"checking");

    //verify the account number
    print("New account: ${myCheckAccount.act_number}");

    //deposit some money
    print("Deposit 100");
    myCheckAccount.deposit(100);
    print("Account amount is:${myCheckAccount.amount}");

    //withdraw some money
    print("Withdraw 10");
    myCheckAccount.withdraw(10);
    //verify the amount left
    print("Account amount is:${myCheckAccount.amount}");
}

We have used Account class to create a new account object, then deposit 100 and then withdraw 10. The final amount is going to be 90. You can run this example on-line and check the output: dart-account

Homework: In the previous examples, add a new test for closing the account with method: closure(). No, this is not a closure function but a function that close the account. Of course we should have made a _status field but we don't have it. So maybe you can add a new field to. Relax and have some fun messing with the code!

To be continued: There is so much more to talk about classes but for now this is all you need to go ahead with the study. I will continue next with collections, that are actually classes. So you will learn more on the go. Later I may add some details about Classes.

Read next: Collections