Java | 原来 try 还可以这样用啊？！

try
{

} catch (Exception e)
{
}

try(...)
{
} catch (Exception e) 
{
}

package org.young.elearn;

import java.io.FileOutputStream;
import java.io.IOException;

import org.junit.Test;

/**
 * try-with-resources 的使用
 * try(resouces)
 * {
 * 
 * } catch (Exception e){}
 * 
 * 这里的resource会自动关闭
 * 
 * 1. resource 必须继承自 java.lang.AutoCloseable
 * 2. 定义和赋值必须都在try里完成
 *
 * @author by Young.ZHU
 *      on 2016年5月29日
 *
 * Package&FileName: org.young.elearn.TryWithResourcesTest
 */
public class TryWithResourcesTest {

/**
 * 验证一下资源是不是真的关闭了
 */
@Test
public void test() {

try (MyResources mr = new MyResources()) {
//mr.doSomething(4);
mr.doSomething(9);
} catch (Exception e) {
System.out.println(e.getMessage());
}
}

/**
 * 编译错误：
 * The resource f of a try-with-resources statement cannot be assigned
 */
@Test
public void test2() {
try (FileOutputStream f = null;) {
//f = new FileOutputStream(new File(""));
} catch (IOException e) {
e.printStackTrace();
}
}

/**
 * 编译错误：
 * The resource type File does not implement java.lang.AutoCloseable
 */
@Test
public void test1() {
/*try (File file = new File("d:\\xx.txt");) {

} */
}

}

class MyResources implements AutoCloseable {

@Override
public void close() throws Exception {
System.out.println("resources are closed.");
}

public void doSomething(int num) throws Exception {
if (num % 2 == 0) {
System.out.println("it's OK.");
} else {
throw new Exception("Enter an even.");
}
}
}