How many Java string objects created in the code String s="abc"+"xyz";?

How many Java string objects will be created in the following statement?

String s = "abc" 开发者_运维知识库+ "xyz"; 

I guess three?

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The compiler creates 1 String per JVM start, because the compiler can determine the resulting String at compile time, it is interned and statically stored in the JVM's String Table.

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FYI, if the statement were concatenating variables (not determinable at runtime), 1 String would be created, but it would create a StringBuilder too. The code would compile to:

new StringBuilder().append(abcVar).append(xyzVar).toString()

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The answer is one global String object per program run, and zero new String objects per statement execution. This is because the Java Language Specification says the expression "abc" + "xyz" is a compile-time constant [0], and that no new String object will be created when the statement is executed [1].

References

[0]: http://java.sun.com/docs/books/jls/third_edition/html/expressions.html#5313

Examples of constant expressions:

"The integer " + Long.MAX_VALUE + " is mighty big."

[1]: http://java.sun.com/docs/books/jls/third_edition/html/expressions.html#15.18.1

If only one operand expression is of type String, then string conversion is performed on the other operand to produce a string at run time. The result is a reference to a String object (newly created, unless the expression is a compile-time constant expression (§15.28)) that is the concatenation of the

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There are three ways to create strings in java

1) we can create a string just by assigning a group of characters to a string type variable

eg:

     String s;  //declare String type variable,  
     s="hello"; //assign a group of characters to it

2)we can create an object to string by allocating memory using new operator.This is just like creating an object to any class.

eg: String s =new String("Hello");

3) We can creating the strings is by converting the character arrays into string.

eg: char arr[] = {'p','r','a','s','h','a','n','t'};