java 使用 callable 传递两个参数并返回参数数组
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Using callable to pass two parameters and returning an array of parameters
提问by Ryan
I have to pass two strings to a thread, which will return an array containing both of them, and I must use callable.
我必须将两个字符串传递给一个线程，该线程将返回一个包含这两个字符串的数组，并且我必须使用 callable。
Here's what I have so far:
这是我到目前为止所拥有的：
public class toArray implements Callable<String[]> {
private String string1 string2;
public toArray (String first, String second)
{
string1= first;
string2 = second;
}
@Override
public String[] call() throws Exception {
String [] allStrings = null;
allStrings[0] = string1;
allStrings[1] = string2;
return allStrings;
}
}
Below is the main:
下面是主要内容：
public class theFuntion{
public static void main(String[] args) {
FutureTask<String[]> task = new FutureTask (new MyCallable());
ExecutorService es = Executors.newSingleThreadExecutor();
es.submit (task);
try{
String[] result = task.get();
System.out.println(result[1] + result[2]);
}
catch(Exception e){
System.err.println(e);
}
es.shutdown();
}
The problem is in main: it says that result is expecting a String[] but it's getting an object. If I cast result it will say an exception must be declared to be thrown.
问题在于main：它说结果需要一个 String[] 但它正在获取一个对象。如果我转换结果，它会说必须声明要抛出异常。
回答by Sal
Change the signature of the class to
将类的签名更改为
public class toArray implements Callable<String[]>
and the signature of the callmethod to
和call方法的签名
public String[] call() throws Exception
UPDATE:Ok, there are more than one error... See the following working sample
更新：好的，有不止一个错误...请参阅以下工作示例
public class Test{
public static void main(String[] args) {
FutureTask<String[]> task = new FutureTask(new MyCallable("a", "b"));
ExecutorService es = Executors.newSingleThreadExecutor();
es.submit (task);
try{
String[] result = task.get();
System.out.println(result[0] + result[1]);
}
catch(Exception e){
System.err.println(e);
}
es.shutdown();
}
public static class MyCallable implements Callable<String[]>
{
private String string1, string2;
public MyCallable (String first, String second)
{
string1= first;
string2 = second;
}
@Override
public String[] call() throws Exception {
String [] allStrings = new String[2];
allStrings[0] = string1;
allStrings[1] = string2;
return allStrings;
}
}
}
回答by Jo?o Silva
In Callable<V>, the parameterized type Vstands for the result type of call(). Since you want to return a String[], instead of Callable<String>, use Callable<String[]>. Then, change the return type of callto String[]:
在 中Callable<V>，参数化类型V代表 的结果类型call()。由于您想返回 a String[]，而不是Callable<String>，请使用Callable<String[]>. 然后，将返回类型更改call为String[]：
@Override
public String[] call() throws Exception {
String [] allStrings = new String[2];
allStrings[0] = string1;
allStrings[1] = string2;
return allStrings;
}
As a side note, class names in Java shouldbe nouns, and should start with an uppercase letter.
作为旁注，Java 中的类名应该是名词，并且应该以大写字母开头。
回答by Reimeus
You have not referenced your ToArrayclass in TheFunction, probably due to compilation errors (hint: fixes have already been mentioned).
您没有在 中引用您的ToArray类TheFunction，可能是由于编译错误（提示：已经提到了修复）。
Your new FutureTask will look like:
您的新 FutureTask 将如下所示：
FutureTask<String[]> task = new FutureTask(new ToArray("foo", "bar"));
Without telling you the bare answer, you will hit 2 exceptions in the call()method in ToArray:
在不告诉您答案的情况下，您将在以下call()方法中遇到 2 个异常ToArray：
- Firstly your String array is never initialised, but shouldbe.
- All arrays start at zero
- 首先，您的 String 数组从未初始化，但应该初始化。
- 所有数组都从零开始
