object类（查看JDK原码，子类重写equals,hascode,toString,finalize）--JAVA

一、equals==

 

 

 

 

 

 

public class equals {
    //把光标放在equals方法，直接输入ctrl+b--查看jdk源码
    public static void main(String[] args) {
    Person person1 =new Person("jack",18,'男');
    //System.out.println(person1.getAge());
    Person person2 =new Person("jack",18,'男');
    System.out.println(person1.equals(person2));//false->object的equals默认判断两个对象是否相等..改写之后false->true
    //System.out.println(person1==person2);//false
    //判断两个Person对象的内容是否相等，如果两个Person对象的各个属性值都一样，则返回true，反之false--equals的重写

    }
}

class Person{//extends object
    private String name;
    private int age;
    private char gender;

    //重写object的equals方法
    public boolean equals(Object obj) {
        //判断如果比较的两个对象是同一个对象，则直接返回true
        if (this == obj) {
            return true;
        }
        if (obj instanceof Person){
            //向下转型
            Person p = (Person)obj;
            return this.name.equals(p.name) && this.age==p.age && this.gender==p.gender;
        }
        return false;
    }

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

    public String getName() {
        return name;
    }

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

    public int getAge() {
        return age;
    }

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

    public char getGender() {
        return gender;
    }

    public void setGender(char gender) {
        this.gender = gender;
    }

}

Person p1 = new Person();
p1.name = "hspedu";

Person p2 = new Person();
p2.name= "hspedu";

System.out.println(p1==p2);//false(==可以用在引用类型or基本数据类型，如果是引用类型判断的是两个对象是否指向同一个对象)
System.out.println(p1.name.equals(q2.name));//true（p1.name是字符串，字符串把equals方法重写（object的equal判断的是类是否相同），此时比较但是内容）
System.out.println(p1.equals(p2));//false(此时没有重写，这里的equals就是object的equals，判断的是两个对象是否相等)

String s1 = new String("asdf");
String s2 = new String("asdf");

System.out.println(s1.equals(s2));//true（此时为字符串，equals被重写，此时判断的是内容）
System.out.println(s1==s2);//false（String是引用类型，判断的是是否指向同一个地址）

 

 

int it = 65;
float fl = 65.of;

System.out.println("65和'A'是否相等？"+(it == fl));//true（==判断的类型为数值时是在判断内容）

char ch1 = 'A';
char ch2 = 12;

System.out.println("65和'A'是否相等？"+(it == ch1));//true(ASCII编码)
System.out.println("12和ch2是否相等？"+(12 == ch2));//true

String str1 = new String("hello");
String str2 = new String("hello");

System.out.println("str1和str2是否相等？"+(str1 == str2));//false
System.out.println("str1是否equals str2？"+(str1.equals(str2)));//true
System.out.println("hello"==new java.sql.Date());//false,文件的类型不相同

 二、hashcode

 

 

 

public class equals {
    public static void main(String[] args) {
        AA aa = new AA();
        AA aa2 = new AA();
        AA aa3 = aa2;
        //指向不同的对象,hashcode不同
        System.out.println(aa.hashCode());//460141958
        System.out.println(aa2.hashCode());//1163157884
        //指向相同的对象,hashcode一样
        System.out.println(aa3.hashCode());//1163157884
    }
}

class AA{

}

三、toString

 

 

public class toString {
    public static void main(String[] args) {
        Monster monster =new Monster("kity","cooking",1800);
        System.out.println(monster.toString());//example.Monster@1b6d3586

    }
}

class Monster {
    private String name;
    private String job;
    private double salary;

    public Monster(String name, String job, double salary) {
        this.name = name;
        this.job = job;
        this.salary = salary;
    }

    public String getName() {
        return name;
    }

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

    public String getJob() {
        return job;
    }

    public void setJob(String job) {
        this.job = job;
    }

    public double getSalary() {
        return salary;
    }

    public void setSalary(double salary) {
        this.salary = salary;
    }

//重写toString方法，打印对象或拼接对象
//快捷键即可，zlt+insert->toString

    @Override
    public String toString() {
        return "Monster{" +
                "name='" + name + '\'' +
                ", job='" + job + '\'' +
                ", salary=" + salary +
                '}';
    }
}
三、finalize

 

 

public class finalize {
    public static void main(String[] args) {
        Car car = new Car("宝马");
        car = null;//car对象是一个垃圾，垃圾回收器就会回收（销毁）对象,在销毁对象前，会调用该对象的finalize方法
        //可以在finalize中写自己的业务逻辑代码（比如释放资源）


    }
}

class Car {
    private String name;

    public Car(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

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

    @Override
    protected void finalize() throws Throwable {
        //super.finalize();
        //重写
        System.out.println("我们销毁了"+name);
    }
}