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Builtin-in Classes in java.lang and java.util Wrapper Classes – Boolean, Character, Byte, Short, Integer – Long, Float, Double String & StringBuffer Vector LinkedList Hashtable 1 Wrapper Classes Wrapper class Primitive Boolean boolean Character char Byte Short Integer Long byte short int long Float Double float double 2 The Integer Class Convert to different types byte double float int long short String byteValue() doubleValue() floatValue() intValue() longValue() shortValue() toString() static String static String static String static String static String toBinaryString(int value) toHexString(int value) toOctalString(int value) toString(int value) toString(int value, int radix) Parse integer strings static Integer static int static int static Integer static Integer decode(String s) parseInt(String s) parseInt(String s, int radix) valueOf(String s) valueOf(String s, int radix) 3 Using the Integer Class public class TestStack { public static void main(String[] args){ Stack s = new Stack(); int i; s.push(new Integer(1)); s.push(new Integer(2)); i = ((Integer)s.pop()).intValue(); System.out.println(s.pop()); } } 4 The Character Class char static int static int static boolean static boolean static boolean static boolean static boolean static boolean static char String static char charValue() digit(char c, int radix) getNumericValue(char c) isDigit(char c) isLetter(char c) isLetterOrDigit(char c) isLowerCase(char c) isSpaceChar(char c) isUpperCase(char c) toLowerCase(char c) toString() toUpperCase(char c) 5 The String Class Defined in java.lang. All string literals are immutable instances of String. – Important: Identical literals have the same object reference. Useful methods include: – charAt, equals, length, startsWith, indexOf, toLowerCase, etc. 6 String Comparisons Several ways to compare two String objects: – compareTo, equals, equalsIgnoreCase. Never use == to test for content equality between strings: – This only gives reference equality. 7 The Immutability of Strings We often construct new strings out of existing strings, e.g., using +. Because String objects are immutable, we always obtain a new instance: – String noun = "dog"; – noun += "s"; Similarly with concat, etc. 8 Parsing Strings public int countSpaces(String s){ int count = 0; // Look for the first. int index = s.indexOf(' '); // indexOf returns -1 on failure. while(index >= 0){ // We found one. count += 1; // Look for the next just after the last one. index = s.indexOf(' ',index+1); } return count; } 9 Strings from Primitive Values Direct assignment is illegal: – String s = 32; // Forbidden. Implicit type conversion is common: – String s = ""+num; Via the static valueOf method: – String s = String.valueOf(num); 10 The StringBuffer Class String-like objects that are mutable. Used for building a String out of multiple pieces. Size is dynamic and unlimited. 11 java.lang.StringBuffer StringBuffer append(xxx arg) where xxx can be any primitive type or objet type StringBuffer insert(int offset, xxx obj) int capacity() char charAt(int index) int length() void setCharAt(int index,char ch) StringBuffer reverse() 12 Formatting an Integer public String formatInt(int number,int width){ // Create space for the full width. StringBuffer formattedInt = new StringBuffer(width); // Append a string version of the number. formattedInt.append(number); // How many extra spaces are required? int spaces = width-formattedInt.length(); for(int i = 0; i < spaces; i++){ formattedInt.insert(0," "); } return formattedInt.toString(); } 13