Question

所以我试图在播放器不存在时显示错误消息，但没有打印出来，我不确定我做错了什么。这是下面的具体代码。

if (mplayer.containsKey("Carlsen, Magnus")) 
    {
  System.out.println("Carlsen, Magnus is on the scoreboard.");
    }
    if (!mplayer.containsKey("Lyons, David")) 
    {
  System.out.println("Lyons, David is not on the scoreboard");
}

感谢任何帮助，我的意思是任何帮助！：）

package javamaptest;


import java.util.*;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

public class JavaMapTest 
{

public static void main(String[] args) 
{

 try
 {
 Map mplayer = new HashMap();

 mplayer.put("Carlsen, Magnus", "Country:NOR,  Rating:(2876),  DOB:1990");
 mplayer.put("Anand, Viswanathan", "Country:IND,  Rating:(2804),  DOB:1969");
 mplayer.put("Caruana, Fabiano", "Country:ITA,  Rating:(2803),  DOB:1992");
 mplayer.put("Nakamura, Hikaru", "Country:USA,  Rating:(2799),  DOB:1987");
 mplayer.put("Topalov, Veselin", "Country:BUL,  Rating(2798), DOB:1975");
 mplayer.put("Grischuk, Alexander", "Country:RUS,  Rating:(2780), DOB:1983");
 mplayer.put("So, Wesley", "Country:USA,  Rating:(2778),  DOB:1993");
 mplayer.put("Kramnik, Vladimir", "Country:RUS,  Rating:(2777),  DOB:1975");
 mplayer.put("Giri, Anish", "Country:NED,  Rating:(2776),  DOB:1994");
 mplayer.put("Aronian, Levon", "Country:ARM,  Rating:(2776),  DOB:1982");
 mplayer.put("Ding, Liren", "Country:CHN,  Rating:(2757),  DOB:1992");
 mplayer.put("Vachier-Lagrave, Maxime", "Country:FRA,  Rating:(2754),  DOB:1990");
 mplayer.put("Karjakin, Sergey", "Country:RUS,  Rating:(2753), DOB:1990");
 mplayer.put("Navara, David", "Country:CZE,  Rating:(2751),  DOB:1985");
 mplayer.put("Tomashevsky, Evgeny", "Country:RUS,  Rating:(2749),  DOB:1987");
 mplayer.put("Li, Chao b", "Country:CHN,  Rating:(2748),  DOB:1989");
 mplayer.put("Woitaszek, Radoslaw", "Country:POL,  Rating:(2746),  DOB:1987");
 mplayer.put("Gelfand, Boris", "Country:ISR,  Rating:(2744),  DOB:1968");
 mplayer.put("Adam, Michael", "Country:ENG,  Rating:(2740),  DOB:1971");
 mplayer.put("Jakovenko, Dmitry", "Country:RUS,  Rating:(2738),  DOB:1983");
// Below I added a pre existing player 
 mplayer.put("Jakovenko, Dmitry", "Country:RUS,  Rating:(2738),  DOB:1983");



Iterator iter = mplayer.entrySet().iterator();

while (iter.hasNext()) 
    {
Map.Entry mEntry = (Map.Entry) iter.next();
System.out.println(mEntry.getKey() + " : " + mEntry.getValue());
}
// This I find a player with a given key
mplayer.get("Carlsen, Magnus");
    mplayer.get("Anand, Viswanathan");

    System.out.println("----------------------------------------------------------------------------");
    System.out.println("Carlson, Magnus key information : " + mplayer.get("Carlsen, Magnus"));
    System.out.println("Anand, Viswanathan key information : " + mplayer.get("Anand, Viswanathan"));
    System.out.println("----------------------------------------------------------------------------");

    if (mplayer.containsKey("Carlsen, Magnus")) 
    {
    System.out.println("Carlsen, Magnus is on the scoreboard.");
    }
    if (!mplayer.containsKey("Lyons, David")) 
    {
    System.out.println("Lyons, David is not on the scoreboard");
    }

 } 

    catch (Exception e) 
    {
 System.out.println(e.toString());
    }

}
}

Answer 1

String testName = "Carlsen, Magnus";
System.out.println(testName + " is " + (mplayer.containsKey(testName) ? "" : "not ") + "on the scoreboard.");

这将输出您正在测试的名称的状态。

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