Allocate yourself some space
Java natively supports 8 fundamental primitive data types:
byte = 8-bit signed integershort = 16-bit signed signed integerint = 32-bit signed integer (the default for integer literals)long = 64-bit signed floating-point numberfloat = 32-bit floating point floating-point numberdouble = 64-bit floating point number (the default for floating point literals)char = 16-bit Unicode character codeboolean = 1-bit true (1) or false (0) valuefloat and double are fundamentally inaccurate. Use java.math.BigDecimal for accuracy.String primitive data type in Java. String is a class that is written in object-oriented Java code.class types, Java is not a purely object-oriented language.The Java API (a set of classes written in Java that are distributed with Java) offers a set of object-oriented utility classes to help manipulate data of the fundamental primitive data types and structures.
ByteShortIntegerLongFloatDoubleCharacterBooleanArraysThe Java API (a set of classes written in Java that are distributed with Java) offers a set of object-oriented utility classes to help manipulate data of the fundamental primitive data types and structures.
ByteShortIntegerLongFloatDoubleCharacterBooleanArraysThese classes are especially helpful when converting a value of one data type to another.
Due to the limitations of working with primitive data types and the conservative nature of the Java API's included Utility/HelperWrapper/ classes, the Apache Software Foundation sponsors a project called Commons Lang that aims to provide functionality that many programmers regret is not present in the Java API. This library includes additional helper classes, such as:
NumberUtilsCharUtilsBooleanUtilsArrayUtilsDue to the limitations of working with primitive data types and the conservative nature of the Java API's included Utility/HelperWrapper/ classes, the Apache Software Foundation sponsors a project called Commons Lang that aims to provide functionality that many programmers regret is not present in the Java API. This library includes additional helper classes, such as:
NumberUtilsCharUtilsBooleanUtilsArrayUtilsCommons Lang is perhaps most well-known for its String-related helper classes: StringUtils, WordUtils, and StringEscapeUtils.
Despite Java's proclamed "Write once, run anywhere" paradigm, writing programs that deal consistently with file paths across Windows, Mac, Linux, and Unix computers is annoying problematic.
Despite Java's proclamed "Write once, run anywhere" paradigm, writing programs that deal consistently with file paths across Windows, Mac, Linux, and Unix computers is annoying problematic.
Example Windows file path:
C:\Users\fernando\Documents\my_file.txtDespite Java's proclamed "Write once, run anywhere" paradigm, writing programs that deal consistently with file paths across Windows, Mac, Linux, and Unix computers is annoying problematic.
Example Windows file path:
C:\Users\fernando\Documents\my_file.txtEquivalent Mac/Unix/Linux file path:
/Users/fernando/Documents/my_file.txtDespite Java's proclamed "Write once, run anywhere" paradigm, writing programs that deal consistently with file paths across Windows, Mac, Linux, and Unix computers is annoying problematic.
Example Windows file path:
C:\Users\fernando\Documents\my_file.txtEquivalent Mac/Unix/Linux file path:
/Users/fernando/Documents/my_file.txtAs you can see, the root of the file path is different (C:\ versus an initial /), and the separator between directories is different (e.g. \ versus /).
Furthermore, the standard string escape character, \ happens to be used in Windows as a file paths. So to avoid that back slash being interpreted as an escape character, it must itself be escaped.
String path = "C:\\Users\\fernando\\Documents\\my_file.txt";Furthermore, the standard string escape character, \ happens to be used in Windows as a file paths. So to avoid that back slash being interpreted as an escape character, it must itself be escaped.
String path = "C:\\Users\\fernando\\Documents\\my_file.txt";This type of problem borders on the absurd.
The Java API offers a "new" solution to this problem in the form of the java.nio.file.Path class, which allows us to deal with file paths in a platform-independent way.
String path = Paths.get("C:", "Users", "fernando", "Documents", "my_file.txt").toString();The Java API offers a "new" solution to this problem in the form of the java.nio.file.Path class, which allows us to deal with file paths in a platform-independent way.
String path = Paths.get("C:", "Users", "fernando", "Documents", "my_file.txt").toString();It also contains useful methods to find out the current working directory, which can be useful for determing the file paths of files in subdirectories of the current working directory:
String cwd = Paths.get("").toAbsolutePath().toString();String another_path = Paths.get(cwd, "data", "my_other_file.txt").toString();The == operator performs a comparison of the position in memory where two values are stored in memory.
String x = "hello";String y = "hello";boolean theSameMemoryAddress = (x == y); // -> most likely true, but not guaranteed to be soThe == operator performs a comparison of the position in memory where two values are stored in memory.
String x = "hello";String y = "hello";boolean theSameMemoryAddress = (x == y); // -> most likely true, but not guaranteed to be soScanner scn = new Scanner(System.in);String x = "hello";String y = scn.nextLine(); // let's imagine the user enters the same text, "hello"...boolean theSameMemoryAddress = (x == y); // -> most likely false!, but not guaranteed to be soString is not a primitive data type, it's an object-oriented class.
== operator may not always result in a true, when comparing two Strings, even those with the same text..equals() method for Strings instead.String x = "hello";String y = "hello";boolean theSameMemoryAddress = x.equals(x); // -> true if they contain the same text, false otherwiseThere is also a StringBuilder class, which is a utility class for the String class.
String is actually fully object-oriented, Strings are immutable.StringBuilder class is a convenient mutable equivalent of the String class.StringBuilder str = new StringBuilder();str.append("goodbye");str.append("foo");str.append("world!");str.delete(7,10); // remove the characters at index positions 7-9, i.e. "foo"str.insert(" ", 7); // insert a space at index position 7str.replace(0, 7, "hello"); // replaces the characters at index positions 0-6 (i.e. "goodbye) with "hello"String result = str.toString(); // -> "hello world!";System.out.println(result);Double dbl = new Double(5.0);int integer = dbl.intValue();String str = Integer.toString(5);// orString str = "" + 5;String str = Double.toString(5.0);String str = Long.toString(50L);String str = Float.toString(5.0F);int i = Integer.valueOf("5").intValue();// orint i = Integer.parseInt("5");double d = Double.valueOf(str).doubleValue();// ordouble d = Double.parseDouble(str);long l = Long.valueOf("5").longValue();// orlong l = Long.parseLong("5");float f = Float.valueOf("5").floatValue();String bin = Integer.toBinaryString(50);String hexstr = Integer.toHexString(50);//orString hexstr = Integer.toString(50, 16);int i = Integer.valueOf("B8DA3", 16).intValue();//orint i = Integer.parseInt("B8DA3", 16);String s = String.valueOf('c');int i = (int) "A";Use exception handline to handle any problems encountered while attempting to convert one data type to another.
String aString = "foo bar baz bum"; // a string that has no obvious int equivalenttry{ // try to do the conversion... i = Integer.parseInt(aString); // will fail and produce an Exception}catch(NumberFormatException e) { // this block of code will run if there was a failure System.out.println(e); // will output the Exception but not crash the program}Now we understand a bit about data types in Java.
Now we understand a bit about data types in Java.
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