js中可以定义生成器函数, 使用yield迭代结果, 例如
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| function* gen() {
yield 1;
yield 2;
yield 3;
}
let g = gen();
g.next();
g.next();
|
本文中尝试在Java环境中实现类似的效果
实现
Generator.java
生成器类
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| import java.util.concurrent.Semaphore;
public class Generator {
private Function function;
private Runnable runnable;
private Thread thread;
private Semaphore readLock;
private Semaphore writeLock;
private Result result;
private Object nextValue;
private boolean done = true;
public Generator(Function function) {
this.function = function;
this.runnable = () -> {
try {
this.writeLock.acquire();
Object value = this.function.run(this);
this.result = new Result(value, true);
this.readLock.release();
} catch (Exception e) {
e.printStackTrace();
}
};
this.reset();
}
public boolean isDone() {
return done;
}
public synchronized void reset() {
this.close();
this.readLock = new Semaphore(0);
this.writeLock = new Semaphore(0);
this.result = null;
this.nextValue = null;
this.done = false;
this.thread = new Thread(this.runnable);
this.thread.start();
}
public synchronized void close() {
if (this.thread != null) {
this.thread.stop();
this.thread = null;
}
}
public synchronized Result next() throws InterruptedException {
return this.next(null);
}
public synchronized Result next(Object value) throws InterruptedException {
if (this.done) {
return null;
}
this.nextValue = value;
this.writeLock.release();
this.readLock.acquire();
Result result = this.result;
this.done = result.isDone();
return result;
}
public Object yield(Object value) throws InterruptedException {
this.result = new Result(value, false);
this.readLock.release();
this.writeLock.acquire();
return this.nextValue;
}
@FunctionalInterface
public interface Function {
Object run(Generator context) throws Exception;
}
public static class Result {
private Object value;
private boolean done;
private Result(Object value, boolean done) {
this.value = value;
this.done = done;
}
public Object getValue() {
return value;
}
public boolean isDone() {
return done;
}
@Override
public String toString() {
return "Result{" +
"value=" + value +
", done=" + done +
'}';
}
}
}
|
测试
Java
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| public class Main {
public static void main(String[] args) throws InterruptedException {
Generator generator = new Generator(context -> {
int count = 0;
for (int i = 0; i < 10; i++) {
Integer value = (Integer) context.yield(i);
count += value == null ? 0 : value;
}
return count;
});
Generator.Result result = null;
do {
result = generator.next(result == null ? null : result.getValue());
System.out.println(result);
} while (!result.isDone());
}
}
|
对应的JavaScript代码
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| let generator = (function* Generator() {
let count = 0;
for (let i = 0; i < 10; i++) {
count += (yield i) || 0;
}
return count;
})();
let result;
do {
result = generator.next(result && result.value);
console.log(result);
} while (!result.done)
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