Some good habits and details of Java ------ updating..., ------ updating

Some good habits and details of Java ------ updating..., ------ updating

1. Do not place the variable on the left side of the Operator During condition determination. This prevents NULL pointer exceptions. Take string comparison as an example:

1 String name = "Tom"; 2 // This method is not recommended. if the variable name is empty, a null pointer exception occurs. 3 if (name. equals ("Tom") {4 // balabala .... 5} 6 // we recommend that you call the equals method of the String constant "Tom" to avoid NULL pointer exceptions. 7 if ("Tom ". equals (name) {8 // balabala9}

2. For Integer type comparison, you must use equals for comparison. If you use = for comparison, the problem may occur. In-128 ~ In the range of 127, the result of using = and equals for Integer is the same. However, if the result exceeds the range of =, an error occurs. Example:

1 Integer a = 128; 2 Integer B = 128; 3 Integer c = new Integer (127); 4 Integer d = 127; 5 Integer e = 127; 6 System. out. println (". equals (B): "+. equals (B); 7 System. out. println ("a = B:" + (a = B); 8 System. out. println ("d. equals (c): "+ d. equals (c); 9 System. out. println ("d = c:" + (d = c); 10 System. out. println ("d = e:" + (d = e ));

Result:

For specific reasons, please refer to the Java Integer Cache Policy [transfer]. In short, it is in-128 ~ The Integer value between 127, using the instance objects included in the cache, instead of creating a new instance.