Java Programming Common Technology (recommended) _java

One: Place the string string in the front

To prevent nullpointerexception exceptions, we typically compare string strings to the left side of the Equals method, which effectively avoids

Null-pointer exception occurred.

In the first case, if variable is NULL, a null-pointer exception occurs, and in the second case, null-pointer exceptions do not occur, and no data is lost, even if variable is null. So suggest

When you are programming, put the direct amount on the left.

Second: Do not trust the early JDK API

In early programming, the JDK API is not very mature, such as the following code block:

File File=new file ("..."), file encapsulates a directory or file, calls the list () method, returns an array of strings if it is a directory, or null if it is not;

So we can add some checksums in advance, as shown in the following code:

Three: Do not believe-1

Explicitly stated in Javadoc string.indexof () If the return value is-1, the character does not exist in the string, or when we read the file using IO stream, it is also defined as-1

Reading is complete. The following code:

It seems to work this way at the moment, but if Java changes the encoding and the definition returns-2 is a better way, it is recommended that the second type be used.

Four: Avoid accidental assignment

The following code:

The first case: the = =, will be an unexpected 5 assignment as a variable, the second case: the situation does not occur unexpected assignment;

The third case: = = = is the same as the exact symbol in JavaScript, the same type, and the value is equal.

Five: Check null and length

Anyway, as long as you have a collection or an array, first make sure it exists and is not empty.

The code is as follows:

The second way is better, avoiding errors in earlier versions of JDK APIs.

Six: All the methods are final.

Prevents subclasses from inheriting all methods of the parent class.

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