Java TWR 语法 Try With Resource

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resource

A resource is an object that must be closed after the program is finished with it.
resource 是一个对象，需要在程序结束前将其关闭。

Java7 之前，如何关闭资源

使用 finally 来确保资源会被关闭。

例如：

public static void main(String[] args) throws Exception {
    InputStream bin = new BufferedInputStream(new FileInputStream("a.txt"));
    try {
        int c;
        while ((c = bin.read()) != -1) {
            System.out.print((char) c);
        }
    } finally {
        bin.close();
    }
}

Java7 开始提供 TWR 语法 Try With Resource

The try-with-resources statement ensures that each resource is closed at the end of the statement.
TWR 语法确保了资源会被自动释放。
Any object that implements java.lang.AutoCloseable, which includes all objects which implement java.io.Closeable
, can be used as a resource.
资源的类需要实现 AutoCloseable 接口。

例如 BufferedInputStream，它的父类 InputStream 实现了 Closeable 接口：

public abstract class InputStream implements Closeable

The Closeable interface extends the AutoCloseable interface.

因此可以通过如下方式使用 BufferedInputStream：
无论是否出现 Exception，bin 都会在 Try 语句块结束时自动释放。

public static void main(String[] args) throws Exception {
    try (InputStream bin = new BufferedInputStream(new FileInputStream("a.txt"))) {
        int c;
        while ((c = bin.read()) != -1) {
            System.out.print((char) c);
        }
    }
}