java多态，equals方法，toString，finalize，断点调试，类变量(方法)注意事项

多态属性重写问题

多态动态绑定机制

package dynamic;

public class A {
    public int i = 10 ;
    public int sum()
    {
        return getI() + 10;
    }
    public int getI()
    {
        return i ;
    }
    public int sum1()
    {
        return i + 10;
    }
}

package dynamic;

public class B extends A{
    public int i = 20 ;
    public int sum()
    {
        return getI() + 20;
    }
    public int getI()
    {
        return i ;
    }
    public int sum1()
    {
        return i + 10;
    }
}

package dynamic;

public class main {
    public static void main(String[] args) {
        A a = new B();
        System.out.println(a.sum());
        System.out.println(a.sum1());

    }
}

多态数组

package dynamicshuzu;

public class main {
    public static void main(String[] args) {
        //继承结构 一个Person 两个学生 两个老师 放在一个数组中
        Person [] persons = new Person[5];
        persons[0] = new Person("jack", 55) ;
        persons[1] = new Student("jack", 22,100) ;
        persons[2] = new Student("jack", 20,50) ;
        persons[3] = new Teacher("jack", 40,2000) ;
        persons[4] = new Teacher("jack", 35,3000) ;
        //循环调用say方法
        for (int i = 0; i < 5; i++) {
            System.out.println(persons[i].say()); // 动态绑定机制
        }
    }
}

package dynamicshuzu;

public class Person {
    private String name ;
    private int age;

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

    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 String say()
    {
       return name + "\t" + age  ;
    }
}

package dynamicshuzu;

public class Student extends Person{
    private double score;

    public Student(String name, int age, double score) {
        super(name, age);
        this.score = score;
    }

    public double getScore() {
        return score;
    }

    public void setScore(double score) {
        this.score = score;
    }

    @Override
    public String say() {
        return super.say() + " score= " + score;
    }
}

package dynamicshuzu;

public class Teacher extends Person{
    private double salary;

    public Teacher(String name, int age, double salary) {
        super(name, age);
        this.salary = salary;
    }

    public double getSalary() {
        return salary;
    }

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

    @Override
    public String say() {
        return super.say() + " salary= " + salary;
    }
}

编译类型和运行类型

.count 看的是编译类型
方法 看的是运行类型

equals方法

package dynamicshuzu;

public class main {
    public static void main(String[] args) {
        Integer int1 = new Integer(1000);
        Integer int2 = new Integer(1000);
        System.out.println(int1 == int2);//false new出的两个地址不一样
        System.out.println(int1.equals(int2));//true 方法重写 判断的是int值 1000

        String s1 = new String("xlx");
        String s2 = new String("xlx");
        System.out.println(s1 == s2);//false new出的两个地址不一样
        System.out.println(s1.equals(s2));//true 方法重写 判断的是string字符串是否一样

    }
}

重写euqals方法

package ex;

public class ex1 {
    public static void main(String[] args) {
        Person person1 = new Person("jack",10,'m');
        Person person2 = new Person("jack",10,'m');
        System.out.println(person1.equals(person2)); // 假 因为不是一个对象 继承的object的equals方法
        //重写之后就会变成true

    }
}
class Person {
    private String name;
    private int age;
    private char gender;

    public boolean equals(Object obj)
    {
        //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;
        //如果传入的是Person类型的话
        if (obj instanceof  Person) {
            Person p = (Person)obj ; // 向下转型
            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;
    }
}

hashCode方法 – 返回对象的哈希表值（简单介绍）

toString

使用快捷键即可
alt + insert 然后找toString（重写后，一般是把对象的自己的属性输出）

finalize

当垃圾回收器确定不存在对该对象的更多引用时，由对象的垃圾回收器调用此方法

断点调试

类变量(方法)注意事项