String trim, length, is empty, and substring
In this chapter you will learn:
- Trim a string, remove the leading and ending spaces
- How to get sub string from a string
- How to check if a string is an empty string
- How to Get the length of a string
Trim a string, remove the leading and ending spaces
String trim() returns a copy of the string, with leading and trailing whitespace omitted.
public class Main {
public static void main(String[] argv) {
String str = " d e m o 2 s.com ";
System.out.println(">"+str+"<");
str = str.trim();//from j av a 2 s . c o m
System.out.println(">"+str+"<");
}
}
The output:
Get sub string from a string
String class has methods to get only part of a string. They are useful
when we want to get specific part of a string. We usually use the indexOf and lastIndexOf
method to get the index first and then use the substring method get the string we are looking for.
CharSequence subSequence(int beginIndex, int endIndex)returns a new character sequence that is a subsequence of this sequence.String substring(int beginIndex)returns a new string that is a substring of this string.String substring(int beginIndex, int endIndex)returns a new string that is a substring of this string.
public class Main {
public static void main(String[] argv) {
String str = "demo2s.com";
System.out.println(str.substring(2));
System.out.println(str.substring(1,3));
}/* j a v a2s.c om*/
}
The output:
if string is empty
boolean isEmpty() returns true if, and only if, length() is 0.
It is useful to check if a string has no value in it, in other words, if a string is "".
However isEmpty would not work if a string object is null.
public class Main {
public static void main(String[] argv) {
String str = "";
System.out.println(str.isEmpty());/*from ja v a 2 s.c o m*/
System.out.println(str.length());
str = "demo2s.com";
System.out.println(str.isEmpty());
System.out.println(str.length());
}
}
The output:
To check if a string object is null, use the following
public class Main {
public static void main(String[] argv) {
String str = "";
System.out.println(str.isEmpty());// j a v a 2 s . c om
System.out.println(str.length());
str = null;
if(str == null){
System.out.println("string is empty");
}
str = "demo2s.com";
System.out.println(str.isEmpty());
System.out.println(str.length());
}
}
Get string length
The length of a string is the number of character in a string.
int length() returns the length of this string.
public class Main {
public static void main(String[] argv) {
String str = "";
System.out.println(str.isEmpty());/*from j av a2s.c o m*/
System.out.println(str.length());
str = "demo2s.com";
System.out.println(str.isEmpty());
System.out.println(str.length());
}
}
The output:
Next chapter...
What you will learn in the next chapter:
- Replaces all occourances of given character with new one and returns new String object
- Replaces only first occourances of given String with new one and returns new String object
- Replaces all occourances of given String with new one and returns new String object
- How to replace escaped string
- Replace \r\n with the <br> tag
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