Java中类中数据域与静态方法不具有多态性，仅有普通的方法调用具有多态性

本文链接：https://blog.youkuaiyun.com/qcladi/article/details/80471457

本文通过一个Java示例程序，展示了如何在父类和子类中处理字段访问及方法覆盖，重点解释了多态性在字段访问上的限制以及方法覆盖的特性。

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类中域与静态方法的调用是在编译期进行解析的，不具有多态性。

在实际的工程中，通常会将域设置为private的，可通过构造get方法返回相应的域，不会直接进行访问；而且，在父类与子类中一般也不会定义名字相同的域。

测试程序如下所示：

package com.naruto.chapter8.FieldAccesstest;

import static net.mindview.util.Print.*;
public class FieldAccess {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Father sup = new Son();
        print("sup.field = " + sup.field + ", sup.getField() = " + sup.getField() + ", ((son)sup).getField() = " + ((Son)sup).getField() + ", ((son)sup).getSuperField() = " + ((Son)sup).getSuperField() + ", ((son)sub).Field = " + ((Son)sup).field);
        print("sup.dataFather = " + sup.dataFather + ", ((Son)sup).dataFather = " + ((Son)sup).dataFather + ", ((Son)sup).dataSon = " + ((Son)sup).dataSon);
        Son sub = new Son();
        print("sub.field = " + sub.field + ", sub.getField() = " + sub.getField() + ", (sub).getField() = " + (sub).getField() + ", ((son)sub).getSuperField() = " + (sub).getSuperField()+ ", ((Father)sub).getField() = " + ((Father)sub).getField()+ ", ((Father)sub).field = " + ((Father)sub).field);
        print("sub.dataFather = " + sub.dataFather + ", ((Father)sub).dataFather = " + ((Father)sub).dataFather + ", (sub).dataSon = " + (sub).dataSon);
    }

}

class Father {
    public int field = 0;
    public String dataFather = "Father Data";
    public int getField() {
        return field;
    }
}

class Son extends Father {
    public int field = 9;
    public String dataSon = "Son Data";
    public int getField() {
        return field;
    }
    public int getSuperField() {
        return super.field;
    }
}

输出：

sup.field = 0, sup.getField() = 9, ((son)sup).getField() = 9, ((son)sup).getSuperField() = 0, ((son)sub).Field = 9
sup.dataFather = Father Data, ((Son)sup).dataFather = Father Data, ((Son)sup).dataSon = Son Data
sub.field = 9, sub.getField() = 9, (sub).getField() = 9, ((son)sub).getSuperField() = 0, ((Father)sub).getField() = 9, ((Father)sub).field = 0
sub.dataFather = Father Data, ((Father)sub).dataFather = Father Data, (sub).dataSon = Son Data