Question

我正在从覆盖旧值的数据库中获取值，怎么知道变量值何时更改。

while(result.next())
{
String rteCd = result.getString("Rte_Cd")
}

每次rteCd都会被数据库值覆盖，我想检查它在哪一点已更改，因为它也可以相同，当它更改时我需要执行一些操作

npte：-我无法更改数据库，查询可以多次返回相同的值

Answer 1

Java.util.Observable可能会有所帮助。如果此对象已更改，则返回java.util.Observable.hasChanged（）方法。这是您可以签出的示例代码

import java.util.Observable;
import java.util.Observer;

class ObservedObject extends Observable {
   private String watchedValue;

   public ObservedObject(String value) {
      watchedValue = value;
   }

   public void setValue(String value) {

      // if value has changed notify observers
      if(!watchedValue.equals(value)) {
         watchedValue = value;

         // mark as value changed
         setChanged();
      }
   }
}
public class ObservableDemo implements Observer {
   public String name;

   public ObservableDemo(String name) {
      this.name = name;
   }

   public static void main(String[] args) {

      // create watched and watcher objects
      ObservedObject watched = new ObservedObject("Original Value");

      // watcher object listens to object change
      ObservableDemo watcher = new ObservableDemo("Watcher");

      // add observer to the watched object
      watched.addObserver(watcher);

      // trigger value change
      System.out.println("setValue method called...");
      watched.setValue("New Value");

      // check if value has changed
      if(watched.hasChanged())
      System.out.println("Value changed");
      else
      System.out.println("Value not changed");
   }

   public void update(Observable obj, Object arg) {
      System.out.println("Update called");
   }
}

输出

setValue方法称为... 值已更改

Answer 2

在while循环之外声明两个以上的变量，然后看到这样的旧值和新值

String oldvalue="";
     String newvalue="";
     while(result.next())
     {
     oldvalue=rteCd;
     String rteCd = result.getString("Rte_Cd")
     newvalue=rteCd;
     }
//Now Display them
println("old value"+oldvalue);
println("new value"+newvalue);

Answer 3

dd(User::find(1)->role);

如何在while循环内检查变量的值是否已更改，而无需在Java内部进行比较

3 个答案: