E' un blog personale dove Francesco Paganelli inserisce dei commenti, considerazioni e osservazioni che riguardano: esperienze vissute, ricerche e studi compiuti, attualità.
23 dicembre 2014
15 dicembre 2014
How compare strings in Java (in-depth examination)
There are two ways:
When using == operator for string comparison you are not comparing the contents of the string but are actually comparing the memory address, if they are both equal it will return true and false otherwise.
Whereas equals in string compares the string contents.
Some examples:
==
tests for reference equality.equals()
tests for value equality
When using == operator for string comparison you are not comparing the contents of the string but are actually comparing the memory address, if they are both equal it will return true and false otherwise.
Whereas equals in string compares the string contents.
Some examples:
// These two have the same value
new String("test").equals("test") // --> true
// ... but they are not the same object
new String("test") == "test" // --> false
// ... neither are these
new String("test") == new String("test") // --> false
// ... but these are because literals are interned by
// the compiler and thus refer to the same object
"test" == "test" // --> true
// concatenation of string literals happens at compile time,
// also resulting in the same object
"test" == "te" + "st" // --> true
// but .substring() is invoked at runtime, generating distinct objects
"test" == "!test".substring(1) // --> false
// interned strings can also be recalled by calling .intern()
"test" == "!test".substring(1).intern() // --> true
How create a temporary table with a select in MySQL
I take note of this simple sintax:
Bye
CREATE TEMPORARY TABLE IF NOT EXISTS temp_table
( INDEX(col_2) ) ENGINE=MyISAM
AS ( SELECT col_1, coll_2, coll_3 FROM mytable )
Bye
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