Detailed explanation of java exception handling examples

This article mainly introduces the detailed introduction and examples of java exception handling. This article summarizes the knowledge level of java exceptions. Friends in need can refer to the

Java exception hierarchy

Exception exception

The difference between RuntimeException and non-RuntimeException exception:

非RuntimeException（检查异常）：在程序中必须使用try…catch进行处理，否则程序无法编译。 
RuntimeException：可以不使用try…catch进行处理，但是如果有异常产生，则异常将由JVM进行处理。
比如：我们从来没有人去处理过NullPointerException异常，它就是运行时异常，并且这种异常还是最常见的异常之一。
出现运行时异常后，系统会把异常一直往上层抛，一直遇到处理代码。如果没有处理块，到最上层，
如果是多线程就由Thread.run()抛出，如果是单线程就被main()抛出。抛出之后，如果是线程，这个线程也就退出了。
如果是主程序抛出的异常，那么这整个程序也就退出了。

The parent classes of the Error class and the Exception class are both throwable classes. The difference between them is:

Error类一般是指与虚拟机相关的问题，如系统崩溃，虚拟机错误，内存空间不足，方法调用栈溢等。
对于这类错误的导致的应用程序中断，仅靠程序本身无法恢复和和预防，遇到这样的错误，建议让程序终止。 
Exception类表示程序可以处理的异常，可以捕获且可能恢复。遇到这类异常，应该尽可能处理异常，
使程序恢复运行，而不应该随意终止异常。

RuntimeException

NullPointException

Generally, Java.lang.NullPointerException is reported for the following reasons:

1. The string variable is not initialized;
2. The object is not initialized with a specific class;

The NullPointException code is as follows:

package TestNullPointException;
public class TestNullPointException {
  public static void main (String[] args) {
    String str = null;
    try {
      if (str.equals(null)) {
        System.out.println("true");
      } else {
        System.out.println("false");
      }
    } catch (NullPointException e) {
      e.printStackTrace();
    }
  }
}

Output:

java.lang.NullPointerException
  at TestNullPointException.TestNullPointException.main(TestNullPointException.java:6)

ArrayIndexOutOfBoundsException exception

Array subscript out-of-bounds exception, when the referenced index value exceeds the length of the array, This exception will occur.

ArrayIndexOutOfBoundsException code is as follows:

package TestArrayIndexOutOfBoundsException;
public class TestArrayIndexOutOfBoundsException {
  public static void main (String[] args) {
    Integer[] array = new Integer[10];
    try {
      Integer temp = array[10];
    } catch (ArrayIndexOutOfBoundsException e) {
      e.printStackTrace();
    }
  }
}

Output:

java.lang.ArrayIndexOutOfBoundsException: 10
  at TestArrayIndexOutOfBoundsException.TestArrayIndexOutOfBoundsException.main(TestArrayIndexOutOfBoundsException.java:6)

ArithmeticException

ArithmeticException is thrown when an abnormal operation condition occurs this exception.

ArithmeticException code is as follows:

/**
 * ArithmeticException
 */

 packet TestArithmeticException;
 public class TestArithmeticException {
  public static void main(String[] args) {
    Integer temp = 1;
    try {
      System.out.println(temp/0);
    } catch (ArithmeticException e) {
      e.printStackTrace();
    }
  }
 }

Output:

java.lang.ArithmeticException: / by zero
  at TestArithmeticException.TestArithmeticException.main(TestArithmeticException.java:6)

ArrayStoreException

When you try to store an object of the wrong type into a Exception thrown when array of objects.

ArrayStoreException code is as follows:

/**
 * ArrayStoreException
 */

 packet TestArrayStoreException;
 public class TestArrayStoreException {
  public static void main(String[] args) {
    Object array = new Integer[10];
    try {
      array[0] = "123";
    } catch (ArrayStoreException e) {
      e.printStackTrace();
    }
  }
 }

Output:

Exception in thread "main" java.lang.ArrayStoreException: java.lang.String
  at TestArrayStoreException.TestArrayStoreException.main(TestArrayStoreException.java:6)

NumberFormatException

Inherits IllegalArgumentException and occurs when a string is converted to a number.

NumberFormatException code is as follows:

/**
 * NumberFormatException
 */
package test;
public class ExceptionTest {
   public static void main(String[] args) { 
      String s = "q12";
      Integer i = Integer.parseInt(s);
   }
 }

Output:

Exception in thread "main" java.lang.NumberFormatException: For input string: "q12"
  at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
  at java.lang.Integer.parseInt(Integer.java:580)
  at java.lang.Integer.parseInt(Integer.java:615)
  at test.ExceptionTest.main(ExceptionTest.java:8)

ClassCastException

Type conversion error, usually when performing forced type conversion error.

ClassCastException code is as follows:

/**
 * ClassCastException 父类赋值给子类，向下转型
 */
package test;
public class ExceptionTest {
   public static void main(String[] args) { 
     Object obj=new Object();
     Integer s=(Integer)obj;
   }
 }

Output:

Exception in thread "main" java.lang.ClassCastException: java.lang.Object cannot be cast to java.lang.Integer
  at test.ExceptionTest.main(ExceptionTest.java:5)

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