异常对象都是派生于Throwable类的一个实例
异常结构
Throwable
ErrorException
IOExceptionRuntimeException
派生于Error和RuntimeException的称为非受查异常，其他的称为受查异常
// 顶层异常类
public class Throwable implements Serializable {}
// Java运行时系统内部错误和资源耗尽
public class Error extends Throwable {}
// 异常
public class Exception extends Throwable {}
// 运行时异常
public class RuntimeException extends Exception {}
// IO异常
public class IOException extends Exception {}
常见Exception
EOFException FileNotFoundException IOException ClassNotFoundException NoSuchFieldException NoSuchMethodException ReflectiveOperationException RuntimeException
常见RuntimeException
ArithmeticException.java ArrayIndexOutOfBoundsException.java ArrayStoreException.java ClassCastException.java EnumConstantNotPresentException.java IllegalArgumentException.java IllegalMonitorStateException.java IllegalStateException.java IllegalThreadStateException.java IndexOutOfBoundsException.java NegativeArraySizeException.java NullPointerException.java NumberFormatException.java SecurityException.java StringIndexOutOfBoundsException.java TypeNotPresentException.java UnsupportedOperationException.java
子类抛出的异常不能比父类更通用声明异常使用throws
public FileInputStream(File file) throws FileNotFoundException {}
抛出异常使用throw
throw new NullPointerException();创建异常类
应该包含无参构造和带有详细信息的参数构造器
public class ExceptionDemo1 extends Exception {
public ExceptionDemo1() {
}
// 能够打印详细信息
public ExceptionDemo1(String message) {
super(message);
}
}
捕获异常
try {
// error
} catch() {
// process error
}
抛出异常和异常链
抛出原始异常，可以使用initCause设置获取原始异常getCause
public static void main(String[] args) {
try {
b();
} catch (Throwable e) {
System.out.println("error = " + e.getMessage());
System.out.println("init cause = " + e.getCause());
}
}
public static void a() {
throw new NullPointerException();
}
public static void b() throws Throwable {
try {
a();
} catch (Exception e) {
Throwable th = new Exception("b methods error");
// 将e设置为原始异常
th.initCause(e);
// 等同于
// Throwable th = new Exception("b methods error", e);
throw th;
}
}
finally
最终一定会被执行的代码块
try {
} catch() {
} finally {
}
finally出现return时，try块的返回无效，因为finally是一定会被执行的，在try中return前就已经执行，所以先返回
public static void main(String[] args) {
System.out.println(a()); // 2
}
static int a() {
try {
return 1;
} finally {
return 2;
}
}
try-with-resource
try块退出时，会自动调用close方法
public static void main(String[] args) {
try (FileInputStream in = new FileInputStream("");
FileOutputStream out = new FileOutputStream("")) {
} catch (Exception e) {
}
}
堆栈轨迹元素
打印异常堆栈printStackTrace获取堆栈数组信息getStackTrace
public static void main(String[] args) {
try {
a();
} catch (Exception e) {
e.printStackTrace();
System.out.println("--------------");
StackTraceElement[] stackTrace = e.getStackTrace();
Stream.of(stackTrace).forEach(System.out::println);
}
}
static void a() {
throw new NullPointerException();
}
java.lang.NullPointerException
at com.java.practice.exception.ExceptionDemo4.a(ExceptionDemo4.java:26)
at com.java.practice.exception.ExceptionDemo4.main(ExceptionDemo4.java:16)
--------------
com.java.practice.exception.ExceptionDemo4.a(ExceptionDemo4.java:26)
com.java.practice.exception.ExceptionDemo4.main(ExceptionDemo4.java:16)
