try-with-resources 语法简介

Posted 2023-01-11

try-with-resources 语法特点

①资源说明头()中可以包含多个定义，用分号隔开（最后的分号可以省略）。资源说明头()中定义的每个对象都会在try块的末尾调用其close()。 ②try-with-resources的try块可以独立存在，没有catch或finally都行。 ③实现了AutoCloseable的类都可以使用try-with-resources。 ④资源说明头()中对象的close()方法调用与创建对象的顺序相反。

案例展示

/**
 * @author 谢阳
 * @version 1.8.0_131
 * @date 2023/1/10 10:51
 * @description
 */
public class TryWithResources 
    public static void main(String[] args) throws NoSuchFieldException, IllegalAccessException, InstantiationException 

        try (
                First first = new First();
                Second second = new Second();
                Third third = new Third()
        ) 
            First.showState();
            Second.showState();
            Third.showState();
            System.out.println("----------------------------------------------");
        
        System.out.println("----------------------------------------------");
        First.showState();
        Second.showState();
        Third.showState();
    



class MyCloseable implements AutoCloseable 
    @Override
    public void close() 
        // 通过反射修改close的值
        try 
            Field field = this.getClass().getDeclaredField("close");
            field.setAccessible(true);
             /*
              setXXX 只适用于基础类，如果对象的字段是包装类采用set(Object obj, Object value)
             */
            field.setBoolean(this.getClass().newInstance(), true); 
         catch (Exception e) 
            e.printStackTrace();
        
        System.out.println(this.getClass().getSimpleName() + "\\tuse close()");
    



class First extends MyCloseable 
    protected static boolean close = false;

    public static void showState() 
        System.out.println(First.class.getSimpleName() + "\\tclose = " + close);
    



class Second extends MyCloseable 
    protected static boolean close = false;

    public static void showState() 
        System.out.println(Second.class.getSimpleName() + "\\tclose = " + close);
    


class Third extends MyCloseable 
    protected static boolean close = false;

    public static void showState() 
        System.out.println(Third.class.getSimpleName() + "\\tclose = " + close);
    

控制台输出