Object class

1. equals()

/* * the difference between equals() and the == operator * * 1, == : operator * 1.1 can be used on base and reference datatype * 1.2 if the base datatype being compared: Compare two basic datatype variables to see if they hold the same data (not necessarily of the same type) * 1.3 If you compare reference datatype: Compare two objects to see if the address value is the same. Whether two references refer to the same object entity * * 2, use of equals() * 1. Public Boolean equals(Object obj) {return (this == obj); public Boolean equals(Object obj) {return (this == obj); } equals() equals() equals() equals() equals() equals() == Things like String, Date, File, and wrapper classes override equals() in Object. When overridden, instead of comparing the address of two references, we compare the "entity content" of two objects. * * 5. In general, our custom classes use equals() to compare whether the "entity contents" of two objects are the same. We need to override equals() in the Object class
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2. toString()

When we print a reference to an Object, we actually call the current Object's toString(), returning the class name and its reference address * * 2.  * public String toString() { return getClass().getName() + "@" + Integer.toHexString(hashCode()); } * * 3. Classes like String, Date, File, and wrapper override the toString() method of the Object class. * Causes the "entity content" information to be returned when the object's toString() is called * * 4. Custom classes can also override the toString() method, which returns the "entity content" of the object */ when called
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// Use the equals() and toString() methods for example:
public class T1equalsAndtoString {

    @Test
    public void test1(a){

        // Basic data type
        int i = 10;
        int j = 10;
        double d = 10.0;
        char c = 10;
        System.out.println(i == c);//true
        System.out.println(i == j);//true
        System.out.println(i == d);//true
        char c1 = 'A';
        int c2 = 65;
        System.out.println(c1 == c2);//true
        System.out.println();


        // Reference the data type
        Customer cust1 = new Customer("abc".12);
        Customer cust2 = new Customer("abc".12);
        System.out.println(cust1 == cust2);//false
        System.out.println(cust1.equals(cust2));// Override equals to compare entity content. true
        System.out.println();


        // Things like String, Date, File, and wrapper classes override equals() in Object
        Date date1 = new Date(32432525324L);
        Date date2 = new Date(32432525324L);
        System.out.println(date1.equals(date2));
        System.out.println();


        Customer cust3 = new Customer("Tom".21);
// 1. When we print a reference to an object, we actually call toString() of the current object, returning the class name and its reference address
        System.out.println(cust3.toString());//com.atguigu.java1.Customer@15db9742-->Customer[name = Tom,age = 21]
        System.out.println(cust3);//com.atguigu.java1.Customer@15db9742-->Customer[name = Tom,age = 21]

        String str = new String("MM");
        System.out.println(str);//MM

        Date date = new Date(4534534534543L);
        System.out.println(date.toString());//Mon Sep 11 08:55:34 GMT+08:00 2113
    }


class Customer{

    private String name;
    private int age;

    public Customer(a) {}public Customer(String name, int age) {
        this.name = name;
        this.age = age;
    }


    public String getName(a) {
        return name;
    }

    public int getAge(a) {
        return age;
    }


    public void setName(String name) {
        this.name = name;
    }

    public void setAge(int age) {
        this.age = age;
    }


// // automatically implements overrides to equals() : CTRL + Shift + S shortcut
// @Override
// public boolean equals(Object o) {
// if (this == o) return true;
// if (! (o instanceof Customer)) return false;
// Customer customer = (Customer) o;
// return getAge() == customer.getAge() &&
// Objects.equals(getName(), customer.getName());
/ /}

    // automatically implement toString()
// @Override
// public String toString() {
// return "Customer{" +
// "name='" + name + '\'' +
// ", age=" + age +
/ / '} ';
/ /}

    / / rewrite the equals ()
    // Overriding principle: compare two objects' entity contents (i.e., name and age) to see if they are the same
    @Override
    public boolean equals(Object obj) {
        //1. Check whether the address value is the same, if the same object, then the entity content must be the same
        if(this == obj){
            return true;
        }

        if(obj instanceof Customer){
            Customer cust = (Customer)obj;
            // Compare whether each attribute of two objects is the same
            //age is the basic data type, compared with ==
            //name is a String, compared with equals in String
            if(cust.age == this.age && cust.name.equals(this.name)){
                return true;
            }else {
                return false; }}else {
            return false; }}}Copy the code

3. hashCode()

It says in the set…

4. clone()

• Shallow copy: When copying an object, only the object itself and its basic variables are copied, without copying the object referred to by the reference contained in the object.
• Deep copy: The deep copy not only copies the object itself, but also all objects that the object contains references to.

/* * 1. Object assignment: two references to the same object * * 2. Clone () shallow copy: The clone() method in Object is protected and returns the Object's * 2.1 implementation * 2.1.1 implementation Cloneable interface, which is a tag interface and has no methods of its own. * 2.1.2 Overwriting the Clone () method, visibility is increased to public * 2.2 Features: Shallow copy only copies the object itself and the basic variables in the object, but does not copy the object containing references to the object * * 3. Clone () deep copy * * 4. The shallow copy example is as follows: */

public class T3clone {

    @Test
    Object assignment: Two references refer to the same object
    public void test1(a) throws Exception {
        Person p1 = new Person("abc".10);
        Person p2 = p1;
        System.out.println(p1 == p2);//true
        p1.setAge(19);
        System.out.println(p2.toString());//Person{name='abc', age=19, address=null}
        System.out.println(p1.toString());//Person{name='abc', age=19, address=null}
    }

    @Test
    // Shallow copy refers to copying only the object itself and the basic variables in the object
    public void test2(a) throws Exception{

        Person p1 = new Person("abc".10);
        Person p3 = (Person) p1.clone();
        System.out.println(p3 == p1);//false
        p3.setName("efg");
        System.out.println(p3.toString());//Person{name='efg', age=10, address=null}
        System.out.println(p1.toString());//Person{name='abc', age=10, address=null}
    }

    @Test
    // Without copying the object containing the reference to the object
    public void teat3(a) throws Exception{

        Address address = new Address("north".110.32);
        Person p4 = new Person("Millet".24, address);
        Person p5 = (Person)p4.clone();
        p5.setAddress(new Address("east".102));
        System.out.println(p4 == p5);//false
        System.out.println(p4.toString());//Person{name=' mi ', age=24, address= address {location='north', distance=110.32}}
        System.out.println(p5.toString());//Person{name=' mi ', age=24, address= address {location='east', distance=102.0}}}}class Person implements Cloneable {

    private String name;
    private int age;
    private Address address;

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public Person(String name, int age, Address address) {
        this.name = name;
        this.age = age;
        this.address = address;
    }

    public void setAddress(Address address) {
        this.address = address;
    }

    public Address getAddress(a) {
        return address;
    }

    public String getName(a) {
        return name;
    }

    public int getAge(a) {
        return age;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setAge(int age) {
        this.age = age;
    }


    @Override
    public String toString(a) {
        return "Person{" +
                "name='" + name + '\' ' +
                ", age=" + age +
                ", address=" + address +
                '} ';
    }

    @Override
    protected Object clone(a) throws CloneNotSupportedException {
        return super.clone(); }}class Address{

    private String location;
    private double distance;

    public String getLocation(a) {
        return location;
    }

    public double getDistance(a) {
        return distance;
    }

    public Address(String location, double distance) {
        this.location = location;
        this.distance = distance;
    }

    public void setLocation(String location) {
        this.location = location;
    }

    public void setDistance(double distance) {
        this.distance = distance;
    }

    @Override
    public String toString(a) {
        return "Address{" +
                "location='" + location + '\' ' +
                ", distance=" + distance +
                '} '; }}Copy the code