大佬，为啥会自动调用toString方法

[一条咸鱼OVO]

代码

为啥最后会去调用toString 不写的话直接输出就会是一串地址。。。。。大佬们

 

package USB1;

import java.util.ArrayList;
import java.util.Collection;

public class Demo000 {
    public static void main(String[] args) {
        Collection col = new ArrayList();
        col.add(new Book("红楼梦", "曹雪芹", 23.1));
        System.out.println(col);

    }
}
class Book{
    private String name;
    private String author;
    private double price;
    public Book (String name , String author , double price){
        this.name = name;
        this.author = author;
        this.price = price;
    }

    public String getName() {
        return name;
    }

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

    public String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }

    @Override
    public String toString() {
        return "Book{" +
                "name='" + name + '\'' +
                ", author='" + author + '\'' +
                ", price=" + price +
                '}';
    }
}