深入拆解 Java 虚拟机 】Exception异常笔记

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try-with-resource语法糖

try后对象的close方法都会被运行。

package com.exception.demo;
public class Foo implements AutoCloseable {private final String name;public Foo(String name) { this.name = name; }@Overridepublic void close() {System.out.println(name);}public static void main(String[] args) {try (Foo foo0 = new Foo("Foo0"); // try-with-resourcesFoo foo1 = new Foo("Foo1");Foo foo2 = new Foo("Foo2")) {System.out.println("ssssss");try {Thread.sleep(3000);} catch (InterruptedException e) {e.printStackTrace();}System.out.println("22222");throw new RuntimeException("Initial");}}
}

start
end
Foo2
Foo1
Foo0
Exception in thread "main" java.lang.RuntimeException: Initialat com.exception.demo.Foo.main(Foo.java:22)

finally

public class Foo2 {private int tryBlock;private int catchBlock;private int finallyBlock;private int methodExit;public void test() {for (int i = 0; i < 100; i++) {try {tryBlock = 0;if (i < 50) {continue;} else if (i < 80) {break;} else {return;}} catch (Exception e) {catchBlock = 1;} finally {finallyBlock = 2;}}methodExit = 3;}
}

对应生成的字节码为

public class com.exception.demo.Foo2 {public com.exception.demo.Foo2();Code:0: aload_01: invokespecial #1                  // Method java/lang/Object."<init>":()V4: returnpublic void test();Code:0: iconst_01: istore_12: iload_13: bipush        1005: if_icmpge     758: aload_09: iconst_010: putfield      #2                  // Field tryBlock:I13: iload_114: bipush        5016: if_icmpge     2719: aload_020: iconst_221: putfield      #3                  // Field finallyBlock:I24: goto          6927: iload_128: bipush        8030: if_icmpge     4133: aload_034: iconst_235: putfield      #3                  // Field finallyBlock:I38: goto          7541: aload_042: iconst_243: putfield      #3                  // Field finallyBlock:I46: return47: astore_248: aload_049: iconst_150: putfield      #5                  // Field catchBlock:I53: aload_054: iconst_255: putfield      #3                  // Field finallyBlock:I58: goto          6961: astore_362: aload_063: iconst_264: putfield      #3                  // Field finallyBlock:I67: aload_368: athrow69: iinc          1, 172: goto          275: aload_076: iconst_377: putfield      #6                  // Field methodExit:I80: returnException table:from    to  target type8    19    47   Class java/lang/Exception27    33    47   Class java/lang/Exception8    19    61   any27    33    61   any47    53    61   any61    62    61   any
}

finally在try、catch后都会运行一次，如果内部还有if等多个分支，那么还会赋值运行多次。

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