Answer:
Prefix 1 matches. Prefix 2 fails. Prefix 3 fails. Prefix 4 matches.
Prefix 1 matches. Prefix 2 fails. Prefix 3 fails. Prefix 4 matches.
String Operations
Here is how the last if of the program worked:
String burns = "My love is like a red, red rose.";
. . . . . .
if ( burns.startsWith( " My love".trim() ) )
System.out.println( "Prefix 4 matches." ); <-- this branch executes
else
System.out.println( "Prefix 4 fails." );
The string " My love" starts with two spaces,
so it does not match the start of the string referenced by burns.
However, its trim() method is called,
which creates a new String without those leading spaces:
if ( burns.startsWith( " My love".trim() ) )
-----+---- -----+-----
| |
| |
| +------- 1. A temporary String object
| is constructed.
| This temporary object
| contains " My love"
|
| 2. The trim() method of the
| temp object is called.
|
| 3. The trim() method returns
| a reference to a SECOND
| temporary String object
| which it has constructed.
| This second temporary
| object contains "My love"
|
| 4. The parameter of the
| startsWith() method
| now is a reference to
| a String, as required.
|
+---- 5. The startsWith() method of
the object referenced by
burns is called.
6. The startsWith() method
returns true
7. The true-branch of the
if-statement executes.
Programmers usually do not think about what happens in such detail.
Usually,
a programmer
thinks:
"trim the spaces of one String and see if it is the prefix of another."
But sometimes,
you need to analyze a statement carefully to be sure it
does what you want.
What does the toLowerCase() method of class String do?