instanceOf 与 isInstance 用法注意事项

package com.cisco.learning;

public class TestInstance {

public static void main(String[] args) {

/*
* false false
*/
/*
* he method returns true if the specified Object argument is non-null
* and can be cast to the reference type represented by this Class
* object without raising a ClassCastException. It returns false
* otherwise.
*/
String str = null;
System.out.println(str instanceof String);
System.out.print(String.class.isInstance(str));

// Error:Incompatible conditional operand types TestInstance and String
/* System.out.println(new TestInstance() instanceof String); */

// Compatible
System.out.println(new Exception() instanceof RuntimeException);
System.out.println(new RuntimeException() instanceof Exception);

System.out.println(String.class.isInstance(new TestInstance()));
System.out.println(RuntimeException.class.isInstance(new Exception()));
System.out.println(Exception.class.isInstance(new RuntimeException()));
System.out.println();

//总结：
/*当实例为null时，都返回false，防止进行转换；
当instanceof，会比较彼此兼容性，且不分左右顺序；*/

}
}