Java类型信息-instanceof、isInstance()、==、equals比较

分手后的思念是犯贱 2023-07-12 11:40 2阅读 0赞

在查询类信息时，instanceof、isInstance()产生的结果相同，==、equals产生的结果相同。示例：

class Parent { }
    class Son extends Parent { }
    public class Test { 
        public static void main(String[] args) { 
            test(new Parent());
            print("\n");
            test(new Son());
        }
    
        private static void test(Object o) { 
            print("Testing o of type:"+o.getClass());
    
            //instanceof
            print("o instanceof Parent:"+(o instanceof Parent));
            print("o instanceof Son:"+(o instanceof Son));
    
            //isInstance
            print("Parent.isInstance(o):"+ Parent.class.isInstance(o));
            print("Son.isInstance(o):"+ Son.class.isInstance(o));
    
            //==
            print("o.getClass == Parent.class :"+(o.getClass()==Parent.class));
            print("o.getClass == Son.class :"+(o.getClass()==Son.class));
    
            //equals
            print("o.getClass.equals(Parent.class) :"+(o.getClass().equals(Parent.class)));
            print("o.getClass.equals(Son.class) :"+(o.getClass().equals(Son.class)));
    
        }
        private static void print(String s){ 
            System.out.println(s);
        }
    }

结果：

Testing o of type:class com.freesky.basic.classt.Parent
    o instanceof Parent:true
    o instanceof Son:false
    Parent.isInstance(o):true
    Son.isInstance(o):false
    o.getClass == Parent.class :true
    o.getClass == Son.class :false
    o.getClass.equals(Parent.class) :true
    o.getClass.equals(Son.class) :false
    
    
    Testing o of type:class com.freesky.basic.classt.Son
    o instanceof Parent:true
    o instanceof Son:true
    Parent.isInstance(o):true
    Son.isInstance(o):true
    o.getClass == Parent.class :false
    o.getClass == Son.class :true
    o.getClass.equals(Parent.class) :false
    o.getClass.equals(Son.class) :true

**instanceof、isInstance()保持了类型的概念，指的是“你是这个类，或者是这个累的派生类吗？”；==、equals比较的是实际的、确切的Class对象，没有考虑继承**