Java starts from scratch, and the basics of learning notes & lt; encapsulation Class & gt; (11)

Introduction to the Integer class: package com. ibm. four; public class Test {public static void main (String [] args) {Integer I = 123; byte b1 = I. byteValue (); System. out. println (b1); double d1 = I. doubleValue (); System. out. println (d1); float f1 = I. floatValue (); int i1 = I. intValue (); long l1 = I. longValue (); short s1 = I. struct value (); String str1 = I. toString (); int ii = 15; int ii1 = Integer. bitCount (ii); System. out. println (ii1 ); Int ii2 = Integer. parseInt (str1, 8); System. out. println (ii2); String str2 = Integer. toBinaryString (ii); System. out. println (str2); String str3 = Integer. toHexString (ii); System. out. println (str3); String str4 = Integer. toString (ii); System. out. println (str4); Integer iii = Integer. valueOf (ii); System. out. println (iii) ;}} String class: some usage methods: package com. ibm. strings; import java. io. unsupportedEncodingExc Eption; public class StringDemo {public static void main (String [] args) throws UnsupportedEncodingException {String str = "welcome softomm"; // method for constructing a new String; // 1. the concat method is added after str! String newStr = str. concat ("! "); System. out. println (newStr); // 2. replace the char value in the String with the new String newStr2 = str. replace ('E', 'E'); System. out. println (newStr2); CharSequence cs = str. subSequence (0, str. length (); CharSequence cs2 = str. subSequence (0, str. length ()/2); String newStr3 = str. replace (cs2, cs); System. out. println (newStr3); // 3. subString truncation // It is used to intercept a new String from the specified index to the end of the String newStr4 = str. substring (8); Sys Tem. out. println (newStr4); // If the str String is truncated to come soft String newStr5 = str. substring (3,12); System. out. println (newStr5); // 4. toUpperCase converts a String into a String newStr6 = str according to the system environment. toUpperCase (); System. out. println (newStr6); // 5. toLowerCase converts String to lowercase String newStr7 = str. toLowerCase (); System. out. println (newStr7); // 6. trim removes the leading and trailing spaces of the string. If there is a space in the middle of the string, the leading space is not removed from the System. out. println (str. trim (); // String SEARCH method String [] Strs = {"a ", "a ", "B ", "aa", "bb", "cc"}; // 1. startWith determines whether a String starts with XX for (String s: strs) {if (s. startsWith ("a") {System. out. println (s);} if (s. endsWith ("handsome") {System. out. println (s + "=========") ;}}// 2. indexof lastIndexOf // determines the index position of the substring that appears for the first time in a string. int index = str. indexOf ('E'); System. out. println (index); // 3. determines the index position of the substring in a string. int last = str. lastIndexOf ('E'); System. out. println (last ); // 4. method for comparing strings // compare this string with another string, case-insensitive //, note that the length of the string and the visiting sequence of each character in the string boolean flag = str. equalsIgnoreCase ("WelCome SofTomM"); System. out. println (flag); // 5. compareTo compares two strings alphabetically. String str8 = "a"; int j = str8.compareTo ("B"); System. out. println (j); // 6. charAt returns the char cc = str. charAt (3); System. out. println (cc); // 7. format: format the string in one format. // 8. getBytes converts a string into a byte array byte [] B = str. getBytes (); // encode and convert a String. If garbled characters exist, run the following command: String newStr9 = new String (str. getBytes ("iso-8859-1"), "UTF-8"); // 9. split Splits a String into one String. String [] stres = str. split (""); System. out. println (stres [0]); System. out. println (stres [1]) ;}} StringBuffer: package com. ibm. strings; public class StringBufferDemo {public static void main (String [] args) {// create a StringBuffer object, representing a variable length String. stringBuffer sb = new StringBuffer (); // call the append method to add the string to the sb object to remove sb. append ("softomm"); sb. append (true); sb. append ("you"); sb. append ("aaaaaaaaa"); // Add "OK" to your backend to become sb. insert (12, "good"); System. out. println (sb); // reverse string reverse AB-> ba sb. reverse (); System. out. println (sb); // setCharAt sets the corresponding string sb for the specified index location. setCharAt (1, 'B'); System. out. println (sb); // setLength specifies the length of sb for a Variable Length string. setLength (2); System. out. println (sb );}} stringBuilder StringBuffer String comparison/* String StringBuffer StringBuilder * variable length * thread safety * efficiency low efficiency Medium efficiency high * single thread support multithreading *** /execution efficiency: package com. ibm. strings; public class StringSpeed {public static void main (String [] args) {// String str = ""; /// obtain the System time in milliseconds. Return the number of milliseconds between and the current time. // long start = System. currentTimeMillis (); // cyclically add an empty str string for 10000 operations // for (int I = 0; I <10000; I ++) {// str = str + I; //} // After the loop is completed, obtain the System time // long end = System. currentTimeMillis (); // System. out. println (end-start); // StringBuffer str = new StringBuffer (); // long start = System. currentTimeMillis (); // cyclically add an empty str string for 10000 operations // for (int I = 0; I <10000; I ++) {// str. append (I); //} // After the loop is completed, obtain the System time // long end = System. currentTimeMillis (); // System. out. println (end-start); StringBuilder str = new StringBuilder (); long start = System. currentTimeMillis (); // cyclically add an empty str string for (int I = 0; I <10000; I ++) {str. append (I);} // After the loop is completed, obtain the System time long end = System. currentTimeMillis (); System. out. println (end-start); // System. out. println (end );}}