class 对象和 java 中的包装器 class 对象有什么区别

Question

通常当我尝试使用 System.out.println();

打印对象时

class Car {
    String color = "red";
}

class Main {
    public static void main(String[] args) {
        Car car = new Car();
        System.out.println(car);
    }
}

输出类似于：

Car@677327b6

也就是它的class name+'@'+hashCode。它在内部调用 toString() 方法。这看起来不错。但是当我按如下方式实现自动装箱时会发生什么：

class Main {
    public static void main(String[] args) {
        int i = 100;
        Integer obj = i;
        System.out.println(obj);
    }
}

这里的输出是100。为什么它不像 Main@hexcode？我以为我正在将原始 i 转换为 Integer 类型的对象。请指正。

Answer 1

Class@hashCode 是 Object.toString(). The Integer class overrides toString().

的默认 return 值

public String toString()
Returns a String object representing this Integer's value. The value is converted to signed decimal representation and returned as a string, exactly as if the integer value were given as an argument to the toString(int) method.

Overrides:
toString in class Object

Returns:
a string representation of the value of this object in base 10.

class 对象和 java 中的包装器 class 对象有什么区别

What is the difference between a normal class object and a wrapper class object in java

java

autoboxing