Go4Expert - Working with Strings in Java

Comparing Strings

To compare strings function equals() is used.

Code: Java

String str1 = "XYZ";
String str2 = "xyz";

boolean result = str1.equals(str2);
boolean result2 = str1.equalsIgnoreCase(str2);

Output

Code: Java

result = false;
result2= true;

String comparison is a common source of bugs for novice Java programmers. A novice programmer will often attempt to compare strings using the comparison operator ==. When used with Strings, the comparison operator == compares object references, not the contents of the object. Because of this, two string objects that contain the same string data, but are physically distinct string object instances, will not compare as equal when using the comparison operator.

Code: Java

String name1 = new String("Timmy");
String name2 = new String("Timmy");

if (name1 == name2) 
{
     System.out.println("The strings are equal.");
}
else 
{
     System.out.println("The strings are not equal.");
}

The output from executing these statements will be

Code:

The strings are not equal.

Now use the equals() method and see the results:

Code: Java

String name1 = new String("Timmy");
String name2 = new String("Timmy");

if (name1.equals(name2)) 
{
     System.out.println("The strings are equal.");
}
else 
{
     System.out.println("The strings are not equal.");
}

The output from executing these statements will be

Code:

The strings are equal.

Searching For and Retrieving Substrings

Code: Java

int result = string1.indexOf(string2);
int result = string1.indexOf(string2, 5);

In the first method shown, the value of result will contain the index of the first occurrence of string2 within string1. If string2 is not contained within string1, -1 will be returned.

In the second method shown, the value of result will contain the index of the first occurrence of string2 within string1 that occurs after the fifth character within string1. The second parameter can be any valid integer greater than 0. If the value is greater than the length of string1, a result of -1 will be returned.

Code: Java

String string1 = "My address is 555 Big Tree Lane";
String address = string1.substring(14);
System.out.println(address);

This code will print out

Code:

555 Big Tree Lane

Processing a String One Character at a Time

Code: Java

for (int index = 0; index < string1.length();index++) 
{
     char aChar = string1.charAt(index);
}

The charAt() method allows you to obtain a single character from the string at the specified index. The characters are indexed 0 based, from 0 to the length of the string-1. The phrase shown previously loops through each character contained in string1.

An alternative method would be to use the StringReader class, as follows:

Code: Java

StringReader reader = new StringReader(string1);
int singleChar = reader.read();

Using this mechanism, the read() method of the StringReader class returns one character at a time, as an integer. Each time the read() method is called, the next character of the string will be returned.

Making a String All Uppercase or All Lowercase

Code: Java

String string = "Contains some Upper and some Lower.";

String string2 = string.toUpperCase();
String string3 = string.toLowerCase();

System.out.println(string2);
System.out.println(string3);

Output

Code:

CONTAINS SOME UPPER AND SOME LOWER.

contains some upper and some lower.