Java基础15-Objects类&System类

package 高级.demo01_Object类;

import java.util.Objects;

public class demo02_Person类 {
    private String name;
    private int age;

    public String getName() {
        return name;
    }

    // 重写Object类的toString方法


    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        // getClass() 使用 反射，等效于instanceof()
        if (o == null || getClass() != o.getClass()) return false;
        demo02_Person类 that = (demo02_Person类) o;
        return age == that.age && Objects.equals(name, that.name);
    }

    @Override
    public int hashCode() {
        return Objects.hash(name, age);
    }

    @Override
    public String toString() {
        return "demo02_Person类{" +
                "name='" + name + ''' +
                ", age=" + age +
                '}';
    }

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

    public int getAge() {
        return age;
    }

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

    public demo02_Person类(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public demo02_Person类() {
    }
}

package 高级.demo01_Object类;

public class demo01_ToString方法 {
    public static void main(String[] args) {
        
        demo02_Person类 p = new demo02_Person类("张三",20);
        String s = p.toString();
        System.out.println(s);
        System.out.println(p); // 获取对象的地址值

    }
}

package 高级.demo01_Object类;

public class demo03_Equals方法 {
    public static void main(String[] args) {
        

        demo02_Person类  p1 = new demo02_Person类("Jack",21);
        demo02_Person类 p2 = new demo02_Person类("Rose",19);

        boolean b = p1.equals(p2);
        System.out.println(b); // false

    }
}

package 高级.demo01_Object类;

import java.util.Objects;

public class demo04_Objects工具类 {
    public static void main(String[] args) {

        String s1 = null;
        String s2 = "abc";

//        boolean b = s1.equals(s2);  空指针异常，null不能调用方法 NullPointerException
//        System.out.println(b);

        boolean b = Objects.equals(s1 ,s2);
        System.out.println(b); // 不报错，容忍空指针，防止空指针异常

        // 源码：
//        public static boolean equals(Object a, Object b) {
//            return (a == b) || (a != null && a.equals(b));
//        }

    }
}

package 高级.demo02_System类;

import java.util.Arrays;

public class demo01_System类 {
    public static void main(String[] args) {

        
        long s = System.currentTimeMillis();
        for (int i = 0; i < 9999; i++) {
            System.out.println(i);
        }
        System.out.println(System.currentTimeMillis()-s);


        

        int[] src = {1,2,3,4,5};
        int[] dest = {6,7,8,9,10};
        System.arraycopy(src,0,dest,0,3);
        System.out.println(Arrays.toString(dest)); //[1, 2, 3, 9, 10]

    }
}