用HashMap在Java中比较带有整数键的关键项

huangapple
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英文:

Comparing Key items with an integer using Hasmap in Java

问题

  1. public class Translate {
  2.     
  3.     Map<Integer, String> map = new HashMap<>();
  4.     private int number;
  6.     {
  7.         map.put(0, "zero");
  8.         map.put(1, "one");
  9.         map.put(2, "two");
  10.         map.put(3, "three");
  11.         map.put(4, "four");
  12.         map.put(5, "five");
  13.         map.put(6, "six");
  14.         map.put(7, "seven");
  15.         map.put(8, "eight");
  16.         map.put(9, "nine");
  17.     }
  19.     public Translate(int number) {
  20.         this.number = number;
  21.     }
  23.     // This is where I'm stuck. I need to compare the Key item to see if it's equal to the integer that is in the Translate constructor.
  24.     public String convertToString() {
  25.         if (map.containsKey(number)) {
  26.             return map.get(number);
  27.         }
  28.         return "";
  29.     }
  30. }
英文:

I'm trying to compare the Key item to see if is equal to the integer that is in the Translate constructor. But someone I can't really figure it out. Sorry for the mess and I' still fairly new to Java. Thanks

  1. public class Translate {
  2.     
  3.         Map&lt;Integer, String&gt; map = new HashMap&lt;&gt;();
  4.         private int number;
  6.         map.put(0, &quot;zero&quot;);
  7.         map.put(1, &quot;one&quot;);
  8.         map.put(2, &quot;two&quot;);
  9.         map.put(3, &quot;three&quot;);
  10.         map.put(4, &quot;four&quot;);
  11.         map.put(5, &quot;five&quot;);
  12.         map.put(6, &quot;six&quot;);
  13.         map.put(7, &quot;seven&quot;);
  14.         map.put(8, &quot;eight&quot;);
  15.         map.put(9, &quot;nine&quot;);
  16.     
  17.         public Translate(int number) {
  18.             this.number = number;
  19.         }
  20.     
  21.         //this is where I&#39;m stuck. I need to compare the Key item to see if is it equal to the integer that is in the Translate constructor. 
  22.         public String convertToString() {
  23.             if (map.get(number) == this.number) {
  24.             };
  25.         }
  26.     }

答案1

得分: 2

  1. 你可以尝试类似这样的写法：
  3.     import java.util.*;
  4.     
  5.     public class Translate {
  6.         
  7.         private static Map<Integer, String> map;
  8.         
  9.         static {
  10.             map = new HashMap<>();
  11.             map.put(0, "zero");
  12.             map.put(1, "one");
  13.             map.put(2, "two");
  14.             map.put(3, "three");
  15.             map.put(4, "four");
  16.             map.put(5, "five");
  17.             map.put(6, "six");
  18.             map.put(7, "seven");
  19.             map.put(8, "eight");
  20.             map.put(9, "nine");
  21.         }
  22.             
  23.         private int number;
  24.         
  25.         public Translate(int number) {
  26.             this.number = number;
  27.         }
  28.         
  29.         public String convertToString() {
  30.             if (map.containsKey(this.number)) {
  31.                 return map.get(this.number);
  32.             }
  33.             return null;
  34.         }
  35.         
  36.         public static void main(String[] args) {
  37.             Translate t = new Translate(7);
  38.             System.out.println(t.convertToString());
  39.         }
  40.     }
英文:

You have to try something like this:

  1. import java.util.*;
  3. public class Translate {
  4.     
  5.     private static Map&lt;Integer, String&gt; map;
  6.     
  7.     static {
  8.         map = new HashMap&lt;&gt;();
  9.         map.put(0, &quot;zero&quot;);
  10.         map.put(1, &quot;one&quot;);
  11.         map.put(2, &quot;two&quot;);
  12.         map.put(3, &quot;three&quot;);
  13.         map.put(4, &quot;four&quot;);
  14.         map.put(5, &quot;five&quot;);
  15.         map.put(6, &quot;six&quot;);
  16.         map.put(7, &quot;seven&quot;);
  17.         map.put(8, &quot;eight&quot;);
  18.         map.put(9, &quot;nine&quot;);
  19.     }
  20.         
  21.     private int number;
  22.     
  23.     public Translate(int number) {
  24.         this.number = number;
  25.     }
  26.     
  27.     public String convertToString() {
  28.         if (map.containsKey(this.number)) {
  29.             return map.get(this.number);
  30.         }
  31.         return null;
  32.     }
  33.     
  34.     public static void main(String[] args) {
  35.         Translate t = new Translate(7);
  36.         System.out.println(t.convertToString());
  37.     }
  38. }

答案2

得分: 1

我不是 Java 的专家，但以下是我发现有问题的部分：

  1. 如果 (map.get(number).equals(this.number)) <--- 这里你正在获取值，而不是键。

    而应该使用 map.contains() 进行检查，如果返回为 true，则返回你传入的键的值。

  2. 你永远不应该使用 "==" 来比较对象，而应该使用该集合的 .equals() 方法，如果有的话。

PS：如果我写错了什么内容，欢迎提供反馈。

英文:

I'm not the expert on java but here is what i found troublesome

if (map.get(number).equals(this.number)) <--- 1.you are fetching the value not the key in this.

Instead check with map.contains() , if returned true by it, return the value of the key you passed.

  1. You should never compare objects with "==" but should instead use .equals() method of that collection , if it is there.

PS: Open for feedback if I wrote something wrong

答案3

得分: 0

  1. public String convertToString() {
  2.   // 只需要判断映射中是否包含这个键，可以使用 containsKey 方法
  3.   if (map.containsKey(this.number)) {
  4.     // 进行其他你想要的操作
  5.   }
  6. }

或者，如果你要在映射中存在值的情况下使用该值，可以省略 containsKey 直接使用 get

  1. public String convertToString() {
  2.   // 返回映射中键为 this.number 的值，如果不存在则返回一个提示信息
  3.   return map.getOrDefault(this.number, "找不到 " + this.number + "！");
  4. }
英文: 
  1. public String convertToString() {
  2.   // You just need to see if the map contains this key, so you can use containsKey
  3.   if (map.containsKey(this.number)) {
  4.     // Do whatever else you want to do
  5.   }
  6. }

Alternatively, if you will use the value in the map if it exists, you can skip the containsKey and just go straight to get

  1. public String convertToString() {
  2.   // Return either the value in the map with key of this.number, or a message that 
  3.   // indicates that no value is present
  4.   return map.getOrDefault(this.number, &quot;Couldn&#39;t find &quot; + this.number + &quot;!&quot;);
  5. }

答案4

得分: 0

你应该首先调用Translate方法并传入任何值。或者，你可以给数字赋予默认值，比如 int number = 5;

然后你可以使用以下代码块：

  1. public String convertToString() {
  2.     if (map.containsKey(this.number)) {
  3.         return map.get(this.number);
  4.     }
  5.     return null;
  6. }

接着，打印该值：System.out.println(t.convertToString());

英文:

You should call Translate method with any value at first. Or, you can give default value to number, such as int number =5;

Then you can use

  1. public String convertToString() {
  2.     if (map.containsKey(this.number)) {
  3.         return map.get(this.number);
  4.     }
  5.     return null;
  6. } method.

Then, print the value System.out.println(t.convertToString());

答案5

得分: 0

请尝试以下代码：

  1. public class Translate {
  3.     private int number;
  5.     Map<Integer, String> map = Map.of(0, "zero", 1, "one", 2, "two", 3, "three", 4, "four", 5, "five", 6, "six", 7, "seven", 8, "eight", 9, "nine");
  7.     public Translate(int number) {
  8.         this.number = number;
  9.     }
  11.     public String convertToString() {
  12.         return map.get(number);  // 如果没有对应的条目，将返回null
  13.     }
  14. }

以上代码如果没有对应的条目，将返回null。或者，您也可以直接返回数字本身：

  1. public String convertToString() {
  2.     return map.getOrDefault(number, Integer.toString(number));
  3. }

如果您想要严格一些，可以在构造函数中针对无效的数字抛出异常：

  1. public Translate(int number) {
  2.     if (!map.containsKey(number)) {
  3.         throw new IllegalArgumentException("number must be 0-9");
  4.     }
  5.     this.number = number;
  6. }
英文:

Try this:

  1. public class Translate {
  3.     private int number;
  5.     Map&lt;Integer, String&gt; map = Map.of(0, &quot;zero&quot;, 1, &quot;one&quot;, 2, &quot;two&quot;, 3, &quot;three&quot;, 4, &quot;four&quot;, 5, &quot;five&quot;, 6, &quot;six&quot;, 7, &quot;seven&quot;, 8, &quot;eight&quot;, 9, &quot;nine&quot;);
  7.     public Translate(int number) {
  8.         this.number = number;
  9.     }
  11.     public String convertToString() {
  12.         return map.get(number);  // returns null if there&#39;s no entry
  13.     }
  14. }

Theabove code rerurns null if there's no entry for the number. Alternatively, you could just return the number itself.

  1. public String convertToString() {
  2.     return map.getOrDefault(number, Integer.toString(number));
  3. }

If you wanted to be strict, you could throw an exception if an invalid number is passed to the constructor:

  1. public Translate(int number) {
  2.     if (!map.containsKey(number)) {
  3.         throw new IllegalArgumentException(&quot;number must be 0-9&quot;);
  4.     }
  5.     this.number = number;
  6. }

huangapple
  • 本文由 发表于 2020年8月31日 12:36:59
  • 转载请务必保留本文链接：https://go.coder-hub.com/63664859.html
  • java
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