Objectives
- Convert a String into a numeric value
- Discuss and use some common String methods
- Discuss and use wrapper classes
parsing and wrapper classes
- Java gets most input as Strings.
- You will often have to convert Strings into numeric values.
- All of the built-in numeric data types have conversion routines to help.
- Assuming you want to convert the String variable strWidth:
- into a byte: byte width = Byte.parseByte(strWidth)
- into a short: short width = Short.parseShort(strWidth)
- into a int: int width = Integer.parseInt(strWidth)
- into a long: long width = Long.parseLong(strWidth)
- into a float: float width = Float.parseFloat(strWidth)
- into a double: double width = Double.parseDouble(strWidth)
- The classes used above to do the conversions are called wrapper classes. They are classes that add additional functionality for each built-in data type (eg. the Integer class for int values).
Strings
- declaring: String name;
- declaring and initializing: String name = "Dave";
- concatenating: String strGreeting = "Hello, " + name;
- displaying: System.out.println(strGreeting);
- displaying: System.out.println("Hello, " + name);
Common Java String methods
| Method | Purpose |
|---|---|
| s1.equals(s2) | returns true or false |
| s1.equalsIgnoreCase(s2) | returns true or false |
| s1.compareTo(s2) | returns an integer less than 0 if s1 is less than s2, greater than 0 if s1 is greater than s2, and equal to 0 if s1 is the same as s2 |
| s1.compareToIgnoreCase(s2) | returns an integer less than 0 if s1 is less than s2, greater than 0 if s1 is greater than s2, and equal to 0 if s1 is the same as s2 |
| s1.toUpperCase() | returns the upper case version of string s1 |
| s1.toLowerCase() | returns the lower case version of string s1 |
| s1.length() | returns the length of string s1 |