Object Class in Java

Object Class in Java

Object class in Java is present in java.lang package. Every class in Java is directly or indirectly derived from the Object class. If a class does not extend any other class then it is a direct child class of the Java Object class and if it extends another class then it is indirectly derived. The Object class provides several methods such as toString(),equals(), hashCode(), and many others. Hence, the Object class acts as a root of the inheritance hierarchy in any Java Program.

Example: Here, we will use the toString() and hashCode() methods to provide a custom string representation for a class.

// Java Code to demonstrate Object class
class Person {
    String n;  //name
    // Constructor
    public Person(String n) {
        this.n = n;
    }
    // Override toString() for a 
    // custom string representation
    @Override
    public String toString() {
        return "Person{name:'" + n + "'}";
    }
    public static void main(String[] args) {
        Person p = new Person("Geek");
        // Custom string representation
        System.out.println(p.toString());//geek
        // Default hash code value
        System.out.println(p.hashCode());//321001045 
    }
}
// Java Code to demonstrate Object class
class Person {
    String n;  //name

    // Constructor
    public Person(String n) {
        this.n = n;
    }

    // Override toString() for a 
    // custom string representation
    @Override
    public String toString() {
        return "Person{name:'" + n + "'}";
    }

    public static void main(String[] args) {

        Person p = new Person("Geek");

        // Custom string representation
        System.out.println(p.toString());//geek

        // Default hash code value
        System.out.println(p.hashCode());//321001045 
    }
}
// Java Code to demonstrate Object class
class Person {
    String n;  //name

    // Constructor
    public Person(String n) {
        this.n = n;
    }

    // Override toString() for a 
    // custom string representation
    @Override
    public String toString() {
        return "Person{name:'" + n + "'}";
    }

    public static void main(String[] args) {

        Person p = new Person("Geek");

        // Custom string representation
        System.out.println(p.toString());//geek

        // Default hash code value
        System.out.println(p.hashCode());//321001045 
    }
}

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Output

Person{name:’Geek’}
321001045

package afterfeb13;
public class Person {
    String n; // name
    // Constructor
    public Person(String n) {
        this.n = n;
    }
    public static void main(String[] args) {
        Person p = new Person("Geek");
        System.out.println(p);// afterfeb13.Person@6e2c634b//cashcode
    }
}
package afterfeb13;

public class Person {
    String n; // name

    // Constructor
    public Person(String n) {
        this.n = n;
    }

    public static void main(String[] args) {

        Person p = new Person("Geek");
        System.out.println(p);// afterfeb13.Person@6e2c634b//cashcode
    }
}
package afterfeb13;

public class Person {
    String n; // name

    // Constructor
    public Person(String n) {
        this.n = n;
    }

    public static void main(String[] args) {

        Person p = new Person("Geek");
        System.out.println(p);// afterfeb13.Person@6e2c634b//cashcode
    }
}

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Output

afterfeb13.Person@6e2c634b

Object Class Methods(TBD)

1. toString() Method

The toString() provides a String representation of an object and is used to convert an object to a String. The default toString() method for class Object returns a string consisting of the name of the class of which the object is an instance, the at-sign character `@’, and the unsigned hexadecimal representation of the hash code of the object.

Note: Whenever we try to print any Object reference, then internally toString() method is called.

Example:

`
public class Student {

    public String toString() {
        return “Student object”;
    }
}
    public String toString() {

        return “Student object”;


    }


}
    public String toString() {

        return “Student object”;


    }


}

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`

Explanation: The toString() method is overridden to return a custom string representation of the Student object.
**

1. hashCode() Method**

For every object, JVM generates a unique number which is a hashcode. It returns distinct integers for distinct objects. A common misconception about this method is that the hashCode() method returns the address of the object, which is not correct. It converts the internal address of the object to an integer by using an algorithm. The hashCode() method is native because in Java it is impossible to find the address of an object, so it uses native languages like C/C++ to find the address of the object.

原文链接：Object Class in Java