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我想知道在 j2me 中是否可以同时打开 2 个或更多的记录存储。我基本上希望能够在代码的同一执行中从 2 个不同的记录存储中添加/删除记录。这可能吗？

如果是这样，你会怎么做？在类的顶部，您执行类似“private RecordStore rs;”之类的操作。您是否需要有两个这样的实例才能使其工作，或者您可以使用一个声明来做到这一点？

提前致谢。

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1 回答 1

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来自RecordStore javadoc：“MIDlet 套件中的 MIDlet 可以创建多个记录存储，只要它们各自被赋予不同的名称。当 MIDlet 套件从平台中删除时，与其 MIDlet 关联的所有记录存储也将被删除. MIDlet 套件中的 MIDlet 可以直接访问彼此的记录存储。”

因此，您可以在一个 MIDlet 中操作多个记录存储。

这是我有时与学生一起使用的示例（警告：此 MIDlet 中没有 UI：仅用于演示目的）。您可以看到使用一两个变量并不重要。

package test;

导入 java.io.ByteArrayInputStream；导入 java.io.ByteArrayOutputStream；导入 java.io.DataInputStream；导入 java.io.DataOutputStream；导入 java.io.IOException；导入 javax.microedition.midlet.*；导入 javax.microedition.rms.RecordEnumeration；导入 javax.microedition.rms.RecordStore；导入 javax.microedition.rms.RecordStoreException；

公共类 ExampleTwoRS 扩展 MIDlet {

private final static String RS_BOYS_NAME = "boys";
private final static String RS_GIRLS_NAME = "girls";

public ExampleTwoRS() {
    Person[] people = new Person[4];
    people[0] = new Person("Angelina", false);
    people[1] = new Person("Brad", true);
    people[2] = new Person("Mirka", false);
    people[3] = new Person("Roger", true);

    try {
        initData(people);
        readData(RS_BOYS_NAME);
        readData(RS_GIRLS_NAME);
    } catch (RecordStoreException ex) {
        ex.printStackTrace();
    } catch (IOException ex) {
        ex.printStackTrace();
    }
}

public void startApp() {
}

private void initData(Person[] people) throws RecordStoreException, IOException {
    RecordStore rsBoys = null;
    RecordStore rsGirls = null;

    try {
        rsBoys = RecordStore.openRecordStore(RS_BOYS_NAME, true);
        rsGirls = RecordStore.openRecordStore(RS_GIRLS_NAME, true);

        for (int i = 0; i < people.length; i++) {
            byte[] data = people[i].toByteArray();
            if (people[i].isMale()) {
                rsBoys.addRecord(data, 0, data.length);
            } else {
                rsGirls.addRecord(data, 0, data.length);
            }
        }
    } finally {
        rsBoys.closeRecordStore();
        rsGirls.closeRecordStore();
    }
}

private void readData(String rsName) throws RecordStoreException, IOException {
    RecordStore rs = null;

    try {
        rs = RecordStore.openRecordStore(rsName, true);

        int i = 0;
        RecordEnumeration re = rs.enumerateRecords(null, null, true);
        Person[] people = new Person[re.numRecords()];
        while (re.hasNextElement()) {
            people[i] = new Person();
            people[i].fromByteArray(re.nextRecord());
            System.out.println(rsName + ": " + people[i].toString());
            i++;
        }
    } finally {
        rs.closeRecordStore();
    }
}

private void initNumbers() {
}

public void pauseApp() {
}

public void destroyApp(boolean unconditional) {
}

}

类人{私人字符串名称；布尔男性；

public Person() {
}

public Person(String name, boolean male) {
    this.name = name;
    this.male = male;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public boolean isMale() {
    return male;
}

public void setMale(boolean male) {
    this.male = male;
}

public void fromDataStream(DataInputStream dis) throws IOException {
    this.name = dis.readUTF();
    this.male = dis.readBoolean();
}

public void toDataStream(DataOutputStream dos) throws IOException {
    dos.writeUTF(getName());
    dos.writeBoolean(isMale());
}

public void fromByteArray(byte[] data) throws IOException {
    ByteArrayInputStream bin = new ByteArrayInputStream(data);
    DataInputStream din = new DataInputStream(bin);

    fromDataStream(din);
    din.close();
}

public byte[] toByteArray() throws IOException {
    ByteArrayOutputStream bout = new ByteArrayOutputStream();
    DataOutputStream dout = new DataOutputStream(bout);

    toDataStream(dout);
    dout.close();

    return bout.toByteArray();
}

public String toString() {
    return name + (male ? " (b)" : " (g)");
}

}

于 2010-03-31T15:51:08.667 回答