JAVA 【引用类型】和【对象类型】在【继承】中的异同

爱被打了一巴掌 2022-03-11 14:40 148阅读 0赞

介绍

JAVA 【引用类型】和【对象类型】在【继承】中的异同，这个问题自己整理过N次，也被人当菜鸟问过N次。所以，在此简单整理一下，以供大家分享。

*  在继承关系中，一般成员变量是根据引用类型
 *  在继承关系中，静态成员变量是根据引用类型
 *  在继承关系中，一般方法是根据对象类型  
    
 *  在继承关系中，静态方法是根据引用类型

注意

静态成员变量，静态方法是基于类的，本文为了测试观察，所以，会用对象去引用静态成员变量和静态方法。

Super Class:

package shuai.study.inherit;
    
    public class SuperClass {
    	public String commonString = "SuperClass Common String";
    	public static String staticString = "SuperClass Static String";
    
    	public int otherCommonInt = 0;
    	public static int otherStaticInt = 10;
    
    	public void commonMethod() {
    		System.out.println("SuperClass Common Method: " + commonString);
    	}
    
    	public static void staticMethod() {
    		System.out.println("SuperClass Static Method: " + staticString);
    	}
    
    	public void otherCommonMethod() {
    		System.out.println("SuperClass Other Common Method: " + otherCommonInt);
    	}
    
    	public static void otherStaticMethod() {
    		System.out.println("SuperClass Other Static Method: " + otherStaticInt);
    	}
    }

Suber Class:

package shuai.study.inherit;
    
    public class SuberClass extends SuperClass {
    	public String commonString = "SuberClass Common String";
    	public static String staticString = "SuberClass Static String";
    
    	@Override
    	public void commonMethod() {
    		System.out.println("SuberClass Common Method: " + commonString);
    	}
    
    	public static void staticMethod() {
    		System.out.println("SuberClass Static Method: " + staticString);
    	}
    }

Test Class:

package shuai.study.inherit;
    
    public class Test {
    
    	public static void main(String[] args) {
    		SuperClass superClass = new SuberClass();
    
    		// Common member variable is according to quote type
    		System.out.println(superClass.commonString);
    
    		// Static member variable is according to quote type
    		// Generally we invoke static member as SuperClass.staticString, because static method & variable is based on class
    		System.out.println(superClass.staticString);
    
    		// Common method is according to object type
    		superClass.commonMethod();
    
    		// Static method is according to quote type
    		// Generally we invoke static method as SuperClass.staticMethod(), because static method & variable is based on class
    		superClass.staticMethod();
    
    		System.out.println("==================================================");
    
    		SuberClass suberClass = new SuberClass();
    
    		// Inherit member variable from super class
    		System.out.println(suberClass.otherCommonInt);
    		System.out.println(SuberClass.otherStaticInt);
    
    		// Inherit method from super class
    		suberClass.otherCommonMethod();
    		SuberClass.otherStaticMethod();
    
    		// Self method
    		suberClass.commonMethod();
    		SuberClass.staticMethod();
    	}
    
    }

Output:

SuperClass Common String
    SuperClass Static String
    SuberClass Common Method: SuberClass Common String
    SuperClass Static Method: SuperClass Static String
    ==================================================
    0
    10
    SuperClass Other Common Method: 0
    SuperClass Other Static Method: 10
    SuberClass Common Method: SuberClass Common String
    SuberClass Static Method: SuberClass Static String