Java reflection (5)-Get inheritance

Directory: The
inheritance relationship can be obtained through the Class object:

1.Class getSuperclass (): Get the parent class type; (single inheritance)
2.Class [] getInterfaces (): Get all the interfaces implemented by the current class; (multiple implementations)
3. Through the isAssignableFrom () method of the Class object, determine whether the Class upward transformation can be achieved.

1. Get the parent class type

public class Main {
    public static void main(String[] args) throws Exception {
        Class i = Integer.class;
        Class n = i.getSuperclass();
        System.out.println(n);
        Class o = n.getSuperclass();
        System.out.println(o);
        System.out.println(o.getSuperclass());
    }
}

Output:

class java.lang.Number 
class java.lang.Object 
null

Integer's parent class is Number, Number's parent class is Object, and Object's parent class is null. Except for Object, any non-interface Class must have a parent type.

2. Get all the interfaces implemented by the current class

public class Main {
    public static void main(String[] args) throws Exception {
        Class s = Integer.class;
        Class[] is = s.getInterfaces();
        for (Class i : is) {
            System.out.println(i);
        }
    }
}

The interfaces implemented by the output Integer are:

java.lang.Comparable
java.lang.constant.Constable
java.lang.constant.ConstantDesc

3. Judging the upward transformation of Class

In non-reflective calls, when we determine whether an instance is of a certain type, under normal circumstances, use the instanceof operator:

Object n = Integer.valueOf(123);
boolean isDouble = n instanceof Double; // false
boolean isInteger = n instanceof Integer; // true
boolean isNumber = n instanceof Number; // true
boolean isSerializable = n instanceof java.io.Serializable; // true

If it is two Class instances, to determine whether an upward transformation is true, you can call isAssignableFrom ():

// Integer i = ?
Integer.class.isAssignableFrom(Integer.class); // true，因为Integer可以赋值给Integer
// Number n = ?
Number.class.isAssignableFrom(Integer.class); // true，因为Integer可以赋值给Number
// Object o = ?
Object.class.isAssignableFrom(Integer.class); // true，因为Integer可以赋值给Object
// Integer i = ?
Integer.class.isAssignableFrom(Number.class); // false，因为Number不能赋值给Integer

Blog source:
https://www.liaoxuefeng.com/wiki/1252599548343744/1264804244564000