Question

我确信这应该很容易，但我已经被困了好几个小时而没有理解这段代码中真正发生的事情：

private void loadUnits() {
        units = new ArrayList<Unit>(); //units is a class global variable
        families = new ArrayList<Family>(); //families is a class global variable
        Statement st;
        Statement stFields;
        ResultSet rs;
        ResultSet rsFields;
        try {
            //Load units info
            st = cnnSrc.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY);
            rs = st.executeQuery(Queries.qUnits);
            while (rs.next()) {
                units.add(new Unit(rs));
            }//END_WHILE
            ConnectionProvider.close(rs, st);

            //First load fields info
            stFields = cnnSrc.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY);
            rsFields = stFields.executeQuery(Queries.qFields);

            //Now load the Family information and create their instances
            st = cnnSrc.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY);
            rs = st.executeQuery(Queries.qFamily);
            while (rs.next()) {
                families.add(new Family(rs, rsFields, units));
                this.debugGlobalParams();
            }//END_WHILE
            ConnectionProvider.close(rsFields, stFields);
            ConnectionProvider.close(rs, st);

        } catch (SQLException ex) {
            LOGGER.error(ex.getMessage(), ex);
        }//END_TRYCATCH
    }//END_METHOD

public void debugGlobalParams() {
        int n = units.size();
        int nu = 0;
        String unitNames = "";
        LOGGER.debug("Debugging " + n + " Units");
        for (int i = 0; i < n; i++) {
            LOGGER.debug(units.get(i).getParkUnitTitleAersa());
        }

        n = families.size();
        LOGGER.debug("Debugging " + n + " Families");
        Family f;
        for (int i = 0; i < n; i++) {
            f = families.get(i);
            LOGGER.debug("FamilyId = " + f.getFamilyId() + "; FamilyTitle = " + f.getFamilyTitle() + "; Tabla = " + f.getTabla());
            nu = f.getUnits().size();
            for (int j = 0; j < nu; j++) {
                unitNames = unitNames + f.getUnits().get(j).getParkUnitTitleAersa() + ",";
            }
            LOGGER.debug("Units included => " + unitNames);
        }
    }//END_METHOD

这个方法被调用一次从DB我的简单域模型，它应该包含一些Family描述和单元描述。每个单元应属于一个且仅属于一个系列，并且该关联在我创建新的Family实例的第二个while期间完成。 Unit构造函数方法很简单，但是要了解Family构造函数中最相关的代码：

public Family(ResultSet rs, ResultSet rsFields, ArrayList<Unit> uns) {
        try {
//Some local variables assignment...
            units = new ArrayList<Unit>();

            int n = uns.size();
            for(int i=0; i<n; i++){
                if(uns.get(i).getFamilyId() == this.FamilyId){
                    this.units.add(uns.get(i));
                }
            }//END_FOR
        } catch (SQLException ex) {
            LOGGER.error(ex.getMessage(), ex);
        }//END_TRYCATCH
    }//END_METHOD

现在，问题在于家庭和他们的正确单位之间的联系没有正确完成，当我打电话给this.debugGlobalParams()时，我发现每个家庭不仅得到他们的单位而且还有以前的家庭。单位。例如，如果我有f1，f2和f3族，并且它们每个都有三个单位u11，u12，u13，u21，u22，u23，u31，u32，u33（其中第一个数字表示它应该与之关联的族）），我应该得到：

f1 -> u11, u12, u13
f2 -> u21, u22, u23
f3 -> u31, u32, u33

但我得到了这个：

f1 -> u11, u12, u13
f2 -> u11, u12, u13, u21, u22, u23
f3 -> u11, u12, u13, u21, u22, u23, u31, u32, u33

我确定问题与参考文献有关但我不明白为什么......有人有什么想法吗？

谢谢！

Answer 1

问题是您的调试显示代码。您将一个系列中的所有单元名称放入unitNames，但不要重置此String。快速破解将重置字符串：

    n = families.size();
    LOGGER.debug("Debugging " + n + " Families");
    Family f;
    for (int i = 0; i < n; i++) {
        unitNames = "";   // <----------- ADD THIS LINE
        f = families.get(i);
        LOGGER.debug("FamilyId = " + f.getFamilyId() + "; FamilyTitle = " + f.getFamilyTitle() + "; Tabla = " + f.getTabla());
        nu = f.getUnits().size();
        for (int j = 0; j < nu; j++) {
            unitNames = unitNames + f.getUnits().get(j).getParkUnitTitleAersa() + ",";
        }
        LOGGER.debug("Units included => " + unitNames);
    }

更好的解决方案是使用迭代器或Iterables，并在循环中声明变量：

for (Family f : families) {
      LOGGER.debug("FamilyId = " + f.getFamilyId() + "; FamilyTitle = " + f.getFamilyTitle() + "; Tabla = " + f.getTabla());

    String unitNames = "";
    for (Unit unit : f.getUnits() {
        unitNames = unitNames + unit.getParkUnitTitleAersa() + ",";
    }
}

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