Lớp Object trong Java | Codelearn

Task

Create the Student class with the following information:

Explanation:

• name, address, gpa attributes describe the name, address and GPA of a Student.
• Student(name: String, address: String, gpa: double) is a. constructor with parameter which is used to initializing attributes.
• toString() is the method which overrides Object class. It returns the object information in the String format. For example, if name = "Kien", address = "Ha Noi", gpa = "6.6", the toString() method will return the following result: "Name: Kien, address: Ha Noi, GPA: 6.6".

A program to test Student class:

public class Entry {
	public static void main(String[] args) {
		Student s = new Student("Kien", "Ha Noi", 6.6);
		System.out.println(s);
	}
}

When the above code is compiled and executed, it produces the following result:

Name: Kien, addres: Ha Noi, GPA: 6.6

Theory

This article will give you better understanding about Object class. First of all, see the following example:

class Student{
}

public class Entry {
	public static void main(String[] args) {
		Student s = new Student();
		System.out.println(s.hashCode());
		System.out.println(s.toString());
		System.out.println(s.getClass());		
	}
}

When the above code is compiled and executed, it produces the following result:

1554547125
[email protected]
class OOP.Student

Looking at the above example, you will wonder why the Student class has methods like hashCode(), toString(), getClass() when you do not declare these methods. The reason is that all classes in Java are inherited from Object class and Object class have these methods

In addition to the above methods, the Object class also has a number of other methods, in which toString() is the method used to represent the object as a string. In fact, the toString() is very useful. For example, when you call the System.out.println() function with an object, the program will display the toString() method of that object:

public class Student {
	private String name;
	private String address;
	private double gpa;

	public Student(String name, String address, double gpa) {
		this.name = name;
		this.address = address;
		this.gpa = gpa;
	}

	@Override
	public String toString() {
		return "Name: " + name + ", address: " + address + ", GPA: " + gpa;
	}
}

When the above code is compiled and executed, it produces the following result:

Name: Kien, age: 23

As you can see, it is possible to use the toString() method instead of the display() method you learned in previous articles.

Instruction

You need to create the Student class like this:

public class Student {
	private String name;
	private String address;
	private double gpa;

	public Student(String name, String address, double gpa) {
		this.name = name;
		this.address = address;
		this.gpa = gpa;
	}

	@Override
	public String toString() {
		return "Name: " + name + ", address: " + address + ", GPA: " + gpa;
	}
}