ArrayList 返回所有条目的最后一项 [英] ArrayList returns last item for all entries

问题描述

我试图用要传递给 ArrayAdapter 的对象填充 ArrayList(最终).我已经提取了一些代码到一个小的测试项目中来说明这个问题.

I am trying to populate an ArrayList with objects to pass to an ArrayAdapter (eventually). I have pulled out some code into a small test project to illustrate the issue.

我有一个名为 Rules 的类，它有两个成员，Gender 和 Age (Rules.Java).在 MyArrayTest 类中，我正在创建规则对象的实例并将它们添加到 rule_parts ArrayList.当我循环遍历数组时，循环执行预期的次数，但会复制最后一个元素.请有人指出原因.

I have a class called Rules which has two members, Gender and Age (Rules.Java). In the class MyArrayTest I am creating instances of Rules objects and adding them to the rule_parts ArrayList. When I loop over the Array the loop executes the expected number of times but duplicates the last element. Please could someone point out why.

Rules.Java

public class Rules {
public static String Gender;
public static Integer Age;


public Rules(String G, Integer C) {
//super();
    Gender = G;
    Age = C;
    }
}

主类 - MyArrayTest.java

Main Class - MyArrayTest.java

import java.util.ArrayList;


public class MyArrayTest {


private static ArrayList<Rules> rule_parts = new ArrayList<Rules>();

public static void main(String[] args) {


// Rules Array  
rule_parts.add(new Rules("Male",25));
rule_parts.add(new Rules("Female",22));

System.out.printf("\n\nRules:\n\n");
for (Rules r : rule_parts) {
    System.out.printf (r.Gender + "\n");
    System.out.printf(r.Age + "\n");


    }

}

}

输出如下:

规则:

女性22

女性22

推荐答案

你需要让 Gender 和 Age 非static 否则这些fields 将只保留每个类成员变量的一个值:

You need to make Gender and Age non-static otherwise these fields will only retain a single value per class member variable:

public String gender;
public Integer age;

旁白: Java 命名约定表明变量以 小写 字母开头，构成 Gender gender 等

Aside: Java naming conventions indicate that variables start with lowercase letters making Gender gender, etc.

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