Programming and Problem Solving with Java

4.2 Conditions and Logical Expressions | 159

Table 4.1 Java Comparison and Case-Conversion Methods

Method Name Argument Type Returns Operation Performed

equals

equalsIgnoreCase

compareTo

toLowerCase

toUpperCase

String

String

String

boolean

boolean

int

String

String

Tests for equality of string

contents.

Returns trueif the strings are

equal, ignoring the case of the

letters. Returns falseif they

are unequal.

Returns 0 if equal, a positive

integer if this string comes

after the string in the

argument, and a negative in-

teger if it comes before the

argument string.

Returns a new identical string

except that the characters are

all lowercase.

Returns a new identical string

except that the characters are

all uppercase.

percase, respectively. The three most useful comparison methods are summarized in Table
4.1, along with toLowerCaseand toUpperCase.
Many of Java’s classes support a method calledcompareTo. As we will see in later chapters,
this common use ofcompareToenables the same piece of code to compare objects of differ-
ent classes. With strings, we often combine the use ofcompareTowith eithertoLowerCaseor
toUpperCase, as we show below. Note thatequalsandequalsIgnoreCasetest only for equality.
We must use thecompareTomethod to test for relationships such as “greater than” or “less than.”
Let’s look at some examples. If lastNameis a Stringvariable, we can write

lastName.equals("Olson") // Tests whether lastName equals "Olson"

Because every Stringliteral is also a Stringobject, Java lets us append the method call to a
literal, if we so choose.

"Olson".equals(lastName) // Tests whether lastName equals "Olson"

As another example, we might write

lastName.compareTo("Olson") > 0 // Tests if lastName comes after "Olson"