System.NullPointerException：尝试取消引用空对象

Question

请帮助我编写代码，我是 Java/SF 新手，我不理解整个代码。

下面的代码应该返回 18 岁以下、18 到 30 岁及以上的人的三个值。

我想学习编码，我评论所有行，如果有错误，请纠正我。

目前我得到错误：

System.NullPointerException：尝试取消引用空对象

Class.testfor1_c.getEZRen：第 18 行，第 1 列 Class.testfor1_c.：第 4 行，第 1 列

public class testfor1_c {

public testfor1_c(ApexPages.StandardController stdcontroller) { 
    getEZRen();
}

public Integer Count_u18 {get; set;} // variable for people < 18
public Integer Count_1830 {get; set;} // variable for people >=18 AND <30
public Integer Count_g30 {get; set;} // variable for people >30

public void getEZRen() {

List<Einzelrisiko__c> EZRList = [SELECT Alter__c FROM Einzelrisiko__c]; // create List EZRList with the information Alter__c of all people

FOR (Einzelrisiko__c EZR : EZRList) {  // Loop thru the all people

    IF(EZR.Alter__c < 18) { Count_u18++; } // if Alter__c < 18 variable Count_u18 increase
    IF(EZR.Alter__c >= 18 && EZR.Alter__c <=30) { Count_1830++; } // if Alter__c >=18 AND <=30 variable Count_1830 increase
    IF(EZR.Alter__c > 30) { Count_g30++; } // if Alter__c > 30 variable Count_g30 increase

}

}

}

<apex:page standardcontroller="account" extensions="testfor1_c">

Anzahl {!Count_u18} // show the value of people <18
Anzahl {!Count_1830} // show the value of people >=18 AND <=30
Anzahl {!Count_g30} // show the value of people >30

</apex:page>

提前致谢， peX

Answer 1

IF(EZR.Alter__c >= 18 && EZR.Alter__c

在这一行你有一个空值。在 if 块中进行比较之前必须使用 check。

Answer 2

你只需要initialize the Integer Properties

public class testfor1_c {

      public testfor1_c(ApexPages.StandardController stdcontroller) { 
          Count_u18 = 0;
          Count_1830 = 0;
          Count_g30 = 0;
          getEZRen();
      }

      public Integer Count_u18 {get; set;} // variable for people < 18
      public Integer Count_1830 {get; set;} // variable for people >=18 AND <30
      public Integer Count_g30 {get; set;} // variable for people >30

      public void getEZRen() {

         List<Einzelrisiko__c> EZRList = [SELECT Alter__c FROM Einzelrisiko__c]; // create List EZRList with the information Alter__c of all people

         for(Einzelrisiko__c EZR : EZRList) {  // Loop thru the all people

               IF(EZR.Alter__c < 18) { Count_u18++; } // if Alter__c < 18 variable Count_u18 increase
               IF(EZR.Alter__c >= 18 && EZR.Alter__c <=30) { Count_1830++; } // if Alter__c >=18 AND <=30 variable Count_1830 increase
              IF(EZR.Alter__c > 30) { Count_g30++; } // if Alter__c > 30 variable Count_g30 increase
         }
      }
}

希望对你有帮助