The difference between string new and direct assignment in Java

String str1= "abc"; and String str2 = new String ("abc"); What's the difference.

String str1= "ABC" might create an object or not create an object, and if the string "ABC" does not exist in the Java string pool, it will create a string object ("abc") in the Java string pool. If it already exists, STR1 direct reference to the object in this string pool.

String str2 = new String ("ABC") creates at least one object, or perhaps two. Because the new keyword is used, a str2 string object is created in the heap, and its value is "ABC". Also, if the string "ABC" does not exist in the Java string pool, it creates a string object in the Java string pool (" ABC ").

String has a intern () method, native, used to detect whether the string exists in the string pool.

Consider the following question:

String str1 = new String ("ABC");
String str2 = new String ("ABC");

STR1 = = is the value of str2 true or false? False.

String STR3 = "ABC";
String STR4 = "ABC";

String STR5 = "A" + "BC";

STR3 = = is the value of STR4 true or false? True.

STR3 = = is the value of STR5 true or false? True.

When writing code, generally do not string str2 = new String ("ABC");

String a = "ABC";
String b= "AB";
String c=b+ "C";
System.out.println (A==C); False
Both A and B are string constants, so they are determined at compile time!

A b in C is a reference not a string constant, so it is not determined at compile time.
And the string is final! So when the B + "C" is actually a new object created, then the reference to the newly created object is passed to C.

This article from Csdn Blog, reproduced please indicate the source: http://blog.csdn.net/kkdelta/archive/2009/03/02/3948725.aspx

The writing is really very detailed, worth learning!

The difference between string new and direct assignment in Java