檢查地圖中的鍵

-3

我有這種方法應該檢查一個鍵是否在地圖中，然後增加一個值。檢查地圖中的鍵

papers.add(paper); //add a paper to the paper collection 
    papersOrdered.get(papers); //returns the papers 
    if(!(papersOrdered.containsKey(paper))) { 
     paperNo = 1; 
     String noPaper = Integer.toString(paperNo); //convert the paperNo integer to a String 
     papersOrdered.put(papers,noPaper); //put the rooNo and the paper collection into the HashMap 
     System.out.println("'" + paper + "'" + " has been added to the paper order. " + noPaper + " copy ordered"); //a message to say a paper has been added 
    } 
    else{ 
     paperNo = paperNo ++; 
     String noPaper = Integer.toString(paperNo); //convert the paperNo integer to a String 
     papersOrdered.put(papers,noPaper); //put the rooNo and the paper collection into the HashMap 
     System.out.println("'" + paper + "'" + " has been added to the paper order." + noPaper + " copies ordered"); //a message to say a paper has been added 
    } 
    System.out.println("======================================================="); ; //a line to seperate text 
    System.out.println(" "); //a blank line

但它不起作用，我不知道爲什麼？

來源

2012-12-14 Jesse Luke Orange

它以什麼方式不起作用？ –

如果您輸入已經在地圖中的鍵，則數字不會增加。 –

'paperNo'從哪裏來？看起來你的問題是'paperNo'不是你從地圖中獲得的數字。（另外，你爲什麼要將整數轉換成字符串和從字符串轉換整數，當你只能使用整數時？） –

根據您的原始代碼，但將整數放入HashMap值而不是字符串中，並且每當爲該類型的紙張添加新訂單時遞增鍵的當前值。

int paperNo; 
String paper; 
HashMap papersOrdered; 
... 
papers.add(paper); //add a paper to the paper collection 
papersOrdered.get(papers); //returns the papers 
if(!(papersOrdered.containsKey(paper))) { 
    paperNo = 1; 
    papersOrdered.put(papers, new Integer(paperNo)); //put the rooNo and the paper collection into the HashMap 
    System.out.println("'" + paper + "'" + " has been added to the paper order. " + paperNo + " copy ordered"); //a message to say a paper has been added 
} else{ 
    paperNo = papersOrdered.get(paper) + 1; //get the current value, and add 1 to it 
    papersOrdered.put(papers, new Integer(paperNo)); //put the rooNo and the paper collection into the HashMap 
    System.out.println("'" + paper + "'" + " has been added to the paper order." + paperNo + " copies ordered"); //a message to say a paper has been added 
} 
System.out.println("======================================================="); ; //a line to seperate text 
System.out.println(" "); //a blank line

來源

2012-12-14 19:02:24 jonhopkins

我第一次嘗試這樣的代碼，我得到一個.put錯誤，但平心而論，我認爲這也會起作用。 –

錯誤說的是什麼？ – jonhopkins

沒有找到合適的方法put（java.util.Array，java.lang.String，int） –

查看Google Guava的Multiset，它完全是這樣。

來源

2012-12-14 19:34:40

檢查地圖中的鍵

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