Question

我想知道在j2me中是否有可能同时打开2个或更多的recordStore。我基本上希望能够在相同的代码执行中添加/删除来自2个不同recordStore的记录。这可能吗？

如果是这样，你会怎么做？在课堂顶部，您可以执行类似'private RecordStore rs;'的操作。你需要有两个这样的实例才能使它工作，或者你能用一个声明吗？

提前致谢。

Answer 1

来自RecordStore javadoc：“MIDlet套件中的MIDlet允许创建多个记录存储，只要它们每个都有不同的名称。当从平台中删除MIDlet套件时，所有与之关联的记录存储它的MIDlet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MIDlet中操作多个记录存储。

以下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）。您可以看到使用一个或两个变量并不重要。

package test;

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

公共类ExampleTwoRS扩展了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) {
}

}

class Person { 私有字符串名称; 布尔男;

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)");
}

}

是否可以在j2me中同时打开和编辑2个或更多RecordStore？

1 个答案: