静态类更新静态变量，但静态方法不更新静态变量

Question

我搜索了几页，但大多数似乎只是对静态的含义有理解问题。我遇到的问题在于我们使用的是静态类、FocusListener 和 ActionListener。具有事件处理调用静态类的类，当一个 JTextfield 被填充并从 FocusListener 中删除时，会立即更新该静态变量。当所有的 JTextfields 都被填满并且 FocusListener 已经更新了变量时，就会出现一个提交 JButton。单击按钮后，将调用静态方法以完成使用先前更新的变量计算的任何变量。用户不知道这一点。但是变量不会更新，我很好奇我是否执行错了？提前致谢。

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;

public class WellParameters extends JInternalFrame implements FocusListener, ActionListener {
    JLabel  measuredDepthL, ..., pitGainL, drillBitSizeL, 
                mudInActivePitsL, mainPanelLabel;
        JTextField  measuredDepthT, ..., pitGainT, drillBitSizeT, mudInActivePitsT;
        JPanel  mainPanel, firstPanel, secondPanel, thirdPanel, fourthPanel, submitButtonPanel;
        JButton submitButton;

        WellParameters() {  
            super("Well Parameters", true, true, false, true);
            this.setBounds(0, 0, 600, 385);
            this.setVisible(true);
            this.setLayout(new BorderLayout());

            ...//GUI Stuff

            this.add(submitButtonPanel, BorderLayout.SOUTH);
        }
    @Override
    public void focusGained(FocusEvent e) {} //Ignore this!

    @Override
    public void focusLost(FocusEvent e) {
        try {
            if(e.getSource() == measuredDepthT) {
                KillWellCalculations.measuredDepth = Integer.parseInt(measuredDepthT.getText());

              ...//Others 

            } else if(e.getSource() == mudInActivePitsT) {
                KillWellCalculations.mudInActivePits = Double.parseDouble(mudInActivePitsT.getText());
            }
        } catch (Exception ignore) {}

    }
    @Override
    public void actionPerformed(ActionEvent e) {
        try {
            if(e.getSource() == submitButton) {
            System.out.println(KillWellCalculations.pumpEfficiency);
            KillWellCalculations.setPressureBeforeCasingBurstAndFormationFracture(); //Doesn't work
            KillWellCalculations.setCirculatingPressures();
            KillWellCalculations.setTriplexPumpCapacity();
            System.out.println(KillWellCalculations.mudInActivePits);
            System.out.println(KillWellCalculations.pumpFactor);
            System.out.println(KillWellCalculations.finalCirculatingPressure);}
        }
        catch(Exception ignore) {}
    }
}

那是 GUI，这是静态类...它们是 2 个独立的类。不在同一个文件中。 打包 killwellsheet;

public class KillWellCalculations {

    static int measuredDepth;           //Total Depth from open hole to bottom

        ... //Tons of other variables

    static double totalStrokes;         //add strokes

    //Used to set different circulating pressures for the well
    public static void setCirculatingPressures() {
        initialCirculatingPressure = circulatingPressureKillRate + shutInDrillPipePressure;
        finalCirculatingPressure = circulatingPressureKillRate * (killMudWeight/currentMudWeight);
    }   
    //Calculates capacity of anypipe
    private static double pipeCapacity(double length, double insideDiameter) {
        return length * ((insideDiameter*insideDiameter)/1029.4);
    }
    //Calculates capacity of the annulus/open hole
    private static double annulusCapacity(double length, double insideDiameter, double outsideDiameter) {
        return length * (((insideDiameter*insideDiameter)-(outsideDiameter*outsideDiameter))/1029.4);
    } 

         ... //Other functions

    //Set the casing burst pressure
    public static void setPressureBeforeCasingBurstAndFormationFracture() {
        beforeCasingBurst = burstPressure*0.70;
        beforeFormationFracture = (0.052*casingShoeDepth)*(fracGradientMWEquivalent - currentMudWeight);
    }
    public static void bariteNeedAndVolumeIncrease() {
        bariteSacksRequired = (totalMudVolume/100)*((1099*(killMudWeight-currentMudWeight))/(28.35-killMudWeight));
        increaseInMudVolume = 0.091*bariteSacksRequired;
    }
    public static void pumpStrokes() {
        surfaceToBit = (mudInDrillString)/pumpFactor;
        bitToSurface = (mudInAnnulus)/pumpFactor;
        totalStrokes = surfaceToBit + bitToSurface;
    }
}//end class

Answer 1

一些澄清...通过阅读您的代码，我唯一看到的是您的类 WellParameters 实现了接口 FocusListener 和 ActionListener（不是静态类）。据我从您的代码中可以看出，方法 focusGained(FocusEvent e) 和 focusLost(FocusEvent e) 是从前一个接口实现的，并更新了静态类，您将依赖于 ActionListener 事件 actionPerformed() 中的相同计算值。您在这里面临的问题是关于静态实例值的竞争条件。

http://java.sun.com/docs/books/performance/1st_edition/html/JPAppGC.fm.html A.3.4 不可达

对象进入不可达状态 当不再强烈引用它时 存在。当一个对象不可达时， 它是收藏的候选者。笔记 措辞：仅仅因为一个对象是 收集的候选人不 意味着它将立即被收集。 JVM可以随意延迟收集 直到有迫切需要 正在消耗的内存 目的。重要的是要注意 不只是任何强有力的参考将 在内存中保存一个对象。这些必须 是从一个链接的引用 垃圾收集根。 GC 根是 一类特殊的变量 包括

堆栈上的临时变量（任何线程的）

静态变量（来自任何类）

来自 JNI 本机代码的特殊引用

根据这个垃圾收集文档，我怀疑你的类 KillWellCalculations 的所有静态引用在调用 FocusEvent 方法后都有资格被垃圾收集，因此，在触发事件 actionPerformed() 时，它们不可用。

只有当这个类被其他类使用时，你仍然可以将 KillWellCalculations 类的静态方法用作实用程序类。如果没有，您可以将其转换为为您保存计算的 Value 类，而无需静态引用。因为您需要引用包含计算值的类的实例......例如：

public Class CalculatedValues {
     private int measuredDepth;
     private double mudInActivePits;

     public static CalculatedValues makeNew() {
          return new CalculatedValues();
     }

     public void setMeasuredDepth(String measuredDepthTString) {
           if (measuredDepthTString == null) {
                throw new IllegalArgumentException("The measured depth must be provided.");
           }
           try {
                this.measuredDepth = Integer.parseInt(measuredDepthTString);
           } catch(NumberFormatException nfe) {
                throw new IllegalArgumentException("The value provided is not an interger.");
           }
     }
     public int getMeasuredDepth() {
          return measuredDepth;
     }

     public void setMudInActivePitsT(String mudInActivePitsTString) {
           if (mudInActivePitsTString == null) {
                throw new IllegalArgumentException("The measured mudInActivePits must be provided.");
           }
           try {
                this.mudInActivePits = Double.parseDouble(measuredDepthTString);
           } catch(NumberFormatException nfe) {
                throw new IllegalArgumentException("The value provided is not an double.");
           }
     }
     public double getMeasuredDepth() {
          return mudInActivePits;
     }

     //...
     //...
     // MORE THE OTHER VALUES/PROPERTIES IMPORTANT/NEEDED BY THE CALCULATION. 

     public void doAllCalculations() {
          // YOU HAVE TO IMPLEMENT THE LOGIC FOR THOSE ONES, OPTIONALLY USING THE SAME UTILITY/HELPER STATIC METHODS FROM 
          setPressureBeforeCasingBurstAndFormationFracture();
          setCirculatingPressures();
          setTriplexPumpCapacity();
     }
}

然后，修改类的构造函数，使其拥有值对象的实例：

... 
...
// THE VALUE OBJECT REFERENCE WITH THE VALUES YOU NEED TO HOLD DURING THE FORM INTERACTION
private CalculatedValues calculatedValues;

WellParameters() {  
    super("Well Parameters", true, true, false, true);
    this.setBounds(0, 0, 600, 385);
    this.setVisible(true);
    this.setLayout(new BorderLayout());

    ...//GUI Stuff

    this.add(submitButtonPanel, BorderLayout.SOUTH);

    // THE VALUE OBJECT REFERENCE...
    calculatedValues = CalculatedValues.makeNew();
}

然后，用计算更新引用：

@Override
public void focusLost(FocusEvent e) {
    try {
        if(e.getSource() == measuredDepthT) { 
            //KillWellCalculations.measuredDepth = Integer.parseInt(measuredDepthT.getText());
            // the exceptions thrown can be caught in the catch below and you can display the error message from the value class.
            calculatedValues.setMeasuredDepth(measuredDepthT.getText());

          ...//Others 

            // collect other values as well...

        } else if(e.getSource() == mudInActivePitsT) {
            //KillWellCalculations.mudInActivePits = Double.parseDouble(mudInActivePitsT.getText());
            // do try/catch for the possible runtime exception and display an error message
            calculatedValues.setMudInActivePitsT(mudInActivePitsT.getText());

        }
    } catch (Exception ignore) { 
    }

}

最后一步的更新也使用实例引用：

  @Override
    public void actionPerformed(ActionEvent e) {
      try {
        if(e.getSource() == submitButton) {
        System.out.println(KillWellCalculations.pumpEfficiency);
        // THE REFERENCES THAT THIS STATIC METHOD USE WERE ALL GARBAGE-COLLECTED AT THE TIME OF THE CALL... IF SHOULD HAVE THE CALCULATED METHODS IN THE VALUE CLASS. SOMETHING LIKE THE FOLLOWING:
        // KillWellCalculations.setPressureBeforeCasingBurstAndFormationFracture(); //Doesn't work
        //KillWellCalculations.setCirculatingPressures();
        //KillWellCalculations.setTriplexPumpCapacity();
        //System.out.println(KillWellCalculations.mudInActivePits);
        //System.out.println(KillWellCalculations.pumpFactor);
        //System.out.println(KillWellCalculations.finalCirculatingPressure);}

        // DO THE FINAL CALCULATION IN A SINGLE METHOD IN THE VALUE OBJECT.
        calculatedValues.doAllCalculations();

        // HERE ARE THE GETTERS FROM THE CALCULATED VALUES OF THE DO ALL CALCULATIONS YOU HAVE TO IMPLEMENT.
        System.out.println(calculatedValues.getMudInActivePits());
        System.out.println(calculatedValues.getPumpFactor());
        System.out.println(calculatedValues.getFinalCirculatingPressure());}

        // CONSIDERING YOU'RE DONE WITH THE VALUES, JUST CLEAR THE INSTANCE VALUES
        // AS THIS REFERENCE IS NOT STATIC AND IT WILL NOT BE GARBAGE-COLLECTED. 
        calculatedValues.clearValues();
    }
    catch(Exception ignore) {}
  }

我做了一些与 GUI 相关的工作...您可以在 http://code.google.com/p/marcellodesales-cs-research/source/browse/trunk/grad-ste-ufpe-brazil/ptf-add-on-dev/src/br/ufpe/cin/stp/ptfaddon/view/swing/execution/JWizardInternalFrame.java 看到一个非常相似的示例

祝你好运！