package FourthExample;

//Here is an example of a simple class called 'Person'. It has two attributes and four methods.

//Note that the attributes are declared private so that they can only be accessed by the methods,

//not by anything outside the class.

//We are also showing the concept of chaining constructors.

// Finally, we're showing an example of a copy constructor where the argument passed to the constructor

// is another Person object of which we then do a copy of the attributes of the original.

class Person {

private String name;

private int age;

public Person() {

System.out.println("Default constructor in chain");

}

// This is the second constructor called in the chain. Note that it calls

// the default constructor last

// and then sets the name.

public Person(String n) {

this();

this.name = n;

}

// This will be the first constructor called in the chain. It then calls the

// second constructor with

// only the name parameter and sets the age itself.

public Person(String n, int a) {

this("Barack Obama");

this.age = a;

}

// This is the copy constructor, notice that we expect another Person object

// and then we copy the

// attributes over.

public Person(Person p) {

this.name = p.name;

this.age = p.age;

}

// Because we're testing for equality, we need to override the equals

// method.

// Note we need to do this because trying to test that o1 == o2 won't return

// the same value if we copy o1 to o2 using the copy constructor.

// Here we test the fields that we're comparing. I.e. if the name and the

// age

// are equal in both objects, then we consider those objects to be equal.

@Override

public boolean equals(Object o) {

if (o == null) {

return false;

}

final Person other = (Person) o;

if (this.name != other.name && this.age != other.age) {

return false;

}

return true;

}

// The general principle is that if we override the equal method, then we

// also need to override

// the default Object hashCode() method. There are many algorithms that can

// be employed

// but we're going with the suggestion by Joshua Bloch in his text book

// Effective Java.

// The idea is that we choose a prime number and repeatedly add that plus

// the field (or, if the

// field is an object, it's hashCode, to the result and return that.

@Override

public int hashCode() {

int prime = 31; // This is some randomly chosen prime number.

int hash = 5; // This is some randomly chosen start value

hash = prime + (this.name != null ? this.name.hashCode() : 0); // Remember

// that

// it is

// possible

// that

// the

// object

// might

// be

// null,

// so we

// check

// that

// so

// that

// we

// don't

// get a

// NullPointerException

// thrown.

hash += prime + this.age;

return hash;

}

int getAge() {

return this.age;

}

String getName() {

return this.name;

}

void setAge(int a) {

this.age = a;

}

void setName(String n) {

this.name = n;

}

}