Question

我制作了一个名为（ObjClass）的自定义类。
我在LinkedHashMap中插入自定义类名而不是值。如下所示：

LinkedHashMap map = new＆lt;＆gt; LinkedHashMap的;
我在ObjClass中有以下getter和setter，名字是

私人字符串名称;

private int level;

private String parent;

现在的问题是，当我尝试通过比较特定字段来获取密钥时，它没有执行。

我的代码如下：

        public class Practice {
     LinkedHashMap<Integer,ObjClass> map = new LinkedHashMap<>();
    public void addd(){
       int a = 10;
            int b = 20;
            int c = 30;
            ObjClass bb = new ObjClass();

bb.setName("COLOR");
       bb.setParent("ROOT");
       bb.setLevel(1);
       bb.getName();
       bb.getParent();
       bb.getLevel();
       map.put(a, bb);

bb.setName("RED");
bb.setParent("COLOR");
bb.setLevel(2);       
bb.getName();
bb.getParent();
bb.getLevel();
map.put(b, bb);

bb.setName("WHITE");
bb.setParent("COLOR");
bb.setLevel(2);        
bb.getName();
bb.getParent();
bb.getLevel();
map.put(c, bb); here



    // the problem is in the for loop i try to get the key of "red" which is 20 but my loop is not working..

    for (Map.Entry<Integer, ObjClass> entry : map.entrySet()) {
        if(entry.getValue().getName().equals("RED"))
        {
            System.out.println("yes"+ entry.getKey());

        }
    }
    System.out.println("    "+map.size());

    }
        public static void main(String[] args) {

               Practice pp = new Practice();
               pp.addd();

    }}

Answer 1

因为您只有一个ObjClass个实例，其名称会被覆盖为WHITE

Answer 2

您只为LinkedHashMap的所有输入提供单个实例。检查更新的代码。

import java.util.LinkedHashMap;
import java.util.Map;

public class Main {
    Map<Integer, ObjClass> lMap  = new LinkedHashMap<>();
    public void addd(){
       int a = 10;
            int b = 20;
            int c = 30;
            ObjClass bb = new ObjClass();

bb.setName("COLOR");
       bb.setParent("ROOT");
       bb.setLevel(1);
       bb.getName();
       bb.getParent();
       bb.getLevel();
       lMap.put(a, bb);

       bb = new ObjClass();       
bb.setName("RED");
bb.setParent("COLOR");
bb.setLevel(2);       
bb.getName();
bb.getParent();
bb.getLevel();
lMap.put(b, bb);

bb = new ObjClass();
bb.setName("WHITE");
bb.setParent("COLOR");
bb.setLevel(2);        
bb.getName();
bb.getParent();
bb.getLevel();
lMap.put(c, bb);


    // the problem is in the for loop i try to get the key of "red" which is 20 but my loop is not working..

    for (Map.Entry<Integer, ObjClass> entry : lMap.entrySet()) {
        //System.out.println(entry.getKey() + "-" + entry.getValue().getName());
        if(entry.getValue().getName().equals("RED"))
        {
            System.out.println("yes"+ entry.getKey());

        }
    }
    System.out.println("    "+lMap.size());

    }
        public static void main(String[] args) {

               Main pp = new Main();
               pp.addd();

    }

}

您需要重新初始化它。

bb = new ObjClass();

Answer 3

在Java中，所有对象变量都是引用。结果你的bb变量被最后一个值改变了。请参阅更正后的代码，如下所示：

import java.util.LinkedHashMap;
import java.util.Map;

public class Practice {
    LinkedHashMap<Integer, ObjClass> map = new LinkedHashMap<>();

    public void addd() {
        int a = 10;
        int b = 20;
        int c = 30;
        ObjClass bb = new ObjClass();

        bb.setName("COLOR");
        bb.setParent("ROOT");
        bb.setLevel(1);
        bb.getName();
        bb.getParent();
        bb.getLevel();
        map.put(a, bb);

        bb = new ObjClass();

        bb.setName("RED");
        bb.setParent("COLOR");
        bb.setLevel(2);
        bb.getName();
        bb.getParent();
        bb.getLevel();
        map.put(b, bb);

        bb = new ObjClass();
        bb.setName("WHITE");
        bb.setParent("COLOR");
        bb.setLevel(2);
        bb.getName();
        bb.getParent();
        bb.getLevel();
        map.put(c, bb);

        // the problem is in the for loop i try to get the key of "red" which is
        // 20 but my loop is not working..

        for (Map.Entry<Integer, ObjClass> entry : map.entrySet()) {
            if (entry.getValue().getName().equals("RED")) {
                System.out.println("yes" + entry.getKey());

            }
        }
        System.out.println("    " + map.size());

    }

    public static void main(String[] args) {

        Practice pp = new Practice();
        pp.addd();

    }
}

另见Is Java “pass-by-reference” or “pass-by-value”?

通过比较LinkedHashMap中的值来获取密钥

3 个答案: