String class in java (video materials from instructor Bi Xiangdong)

Package cn. itcast. p1.string. demo; public class StringDemo {/*** @ param args */public static void main (String [] args) {// TODO Auto-generated method stub/** features of the String class: * The String object will not be changed once initialized. **/StringDemo2 ();} public static void stringDemo2 () {// TODO Auto-generated method stubString s = "abc"; // create a String object in the constant pool. String s1 = new String ("abc"); // create two objects. One is new and the other is in heap memory. System. out. println (s = s1); // falseSystem. out. println (s. equals (s1); // equals in the string class describes the equals in the Object to establish the basis for the string class to determine whether the string Object is the same. // Compare the string content. // System. out. println ("s =" + s); // System. out. println ("s1 =" + s1);}/*** demonstrates the first method of string definition and clarifies the characteristics of the String constant pool. * If the pool does not exist, it is created and used directly. */Private static void stringDemo1 () {String s = "abc"; // "abc" is stored in the String constant pool. // S = "nba"; String s1 = "abc"; System. out. println (s = s1); // true? // System. out. println ("s =" + s );}}

Package cn. itcast. p1.string. demo; public class StringConstructorDemo {/*** @ param args */public static void main (String [] args) {// TODO Auto-generated method stub/** you can use the String constructor to convert a byte array or character array into a String. */StringConstructorDemo2 ();} private static void stringConstructorDemo2 () {char [] arr = {'w', 'A', 'P', 'Q ', 'X'}; String s = new String (arr, 1, 3); System. out. println ("s =" + s);} public static void stringConstructorDemo () {String s = new String (); // equivalent to String s = ""; not equivalent to String s = null; byte [] arr = {97,66, 67,68}; String s1 = new String (arr); System. out. println ("s1 =" + s1 );}}

Package cn. itcast. p1.string. demo; public class StringMethodDemo {/*** @ param args */public static void main (String [] args) {/** function classification of strings based on object-oriented ideas. * "Abcd" ** 1, get: * 1.1 get the number (length) of Characters in the string. * int length (); * 1.2 get characters by position. * Char charAt (int index); * 1.3 obtain the position of the first occurrence of the character in the string based on the character. * int indexOf (int ch) * int indexOf (int ch, int fromIndex): searches for the first occurrence location of ch from the specified position * int indexOf (String str ); * int indexOf (String str, int fromIndex); * obtain the first position in the String based on the String. * int lastIndexOf (int ch) * int lastIndexOf (int ch, int fromIndex): searches for the first occurrence location of ch from the specified location * int lastIndexOf (String str ); * int lastIndexOf (String str, int fromIndex); * 1.4 obtain one of the strings Some strings. It is also called a substring. * String substring (int beginIndex, int endIndex) // contains begin and does not contain end. * String substring (int beginIndex); ***** 2, conversion. * 2.1 convert a String into a String Array (String cutting) * String [] split (String regex): involves regular expressions. * 2.2 convert a String into a character array. * Char [] toCharArray (); * 2.3 converts a string into a byte array. * Byte [] getBytes (); * 2.4 converts letters in a string into uppercase and lowercase letters. * String toUpperCase (): uppercase * String toLowerCase (): lowercase * 2.5 replace the content in the String * String replace (char oldch, char newch); * String replace (String s1, string s2); * 2.6 removes spaces at both ends of the String. * String trim (); * 2.7 concatenates strings. * String concat (string); ** 3: determines if the content of the String * 3.1 is the same? * Boolean equals (Object obj); * boolean compare signorecase (string str); the upper-case comparison string content is ignored. * Does the 3.2 string contain the specified string? * Boolean contains (string str); * Indicates whether a 3.3 string starts with a specified string. Whether to end with a specified string. * Boolean startsWith (string); * boolean endsWith (string); ** 4, comparison. **/StringMethodDemo_4 (); // System. out. println ("abc ". concat ("kk"); // System. out. println ("abc" + "kk"); // System. out. println (String. valueOf (4) + 1); // System. out. println ("" + 4 + 1);} private static void stringMethodDemo_4 () {System. out. println ("abc ". compareTo ("aqz");} private static void stringMethodDemo_3 () {String s = "abc"; System. out. println (s. equals ("ABC ". toLowerCase (); System. out. println (s. equalsIgnoreC Ase ("ABC"); System. out. println (s. contains ("cc"); String str = "ArrayDemo. java "; System. out. println (str. startsWith ("Array"); System. out. println (str. endsWith (". java "); System. out. println (str. contains ("Demo");} private static void stringMethodDemo_2 () {String s = "Zhang San, Li Si, Wang Wu"; String [] arr = s. split (","); for (int I = 0; I <arr. length; I ++) {System. out. println (arr [I]);} char [] chs = s. toCharArray (); for (I Nt I = 0; I <chs. length; I ++) {System. out. println (chs [I]);} s = "AB "; byte [] bytes = s. getBytes (); for (int I = 0; I <bytes. length; I ++) {System. out. println (bytes [I]);} System. out. println ("Abc ". toUpperCase (); String s1 = "java"; String s2 = s1.replace ('Q', 'z'); System. out. println (s1 = s2); // trueSystem. out. println ("-" + "AB c ". trim () + "-");} private static void stringMethodDemo_1 () {String s = "abcdae "; System. out. println ("length:" + s. length (); // 6System. out. println ("char:" + s. charAt (2); // c // StringIndexOutOfBoundsExceptionSystem. out. println ("index:" + s. indexOf ('k'); // 0 //-1 we can determine whether the character or string exists based on-1. System. out. println ("lastIndex:" + s. lastIndexOf ('A'); // 4System. out. println ("substring:" + s. substring (2, 4 ));}}

Package cn. itcast. p1.string. demo; public class StringObjectDemo {/*** @ param args */public static void main (String [] args) {// String s1 = "abc "; // String s2 = "abc"; // intern (): String s1 = new String ("abc"); String s2 = s1.intern (); system. out. println (s1 = s2); // false }}