java字符串.ppt

第6章字符串
String是类,不是数组,也不是基本数据类型
String定义为final class,使用了copy on write技术
1)String的初始化
String str = new String(“hello”);
String str = “hello”;
2) String对象和String引用
String str1 = new String(“hello”);
String str2 = new String(“hello”);
boolean b = (str1==str2);
boolean b = (str2);
3)new和直接赋值的区别
String str1 = “hello”;
String str2 = “hello”;
boolean b = (str1==str2);
boolean b = (str2);
String VS StringBuffer
当字符串不大会改变的时候使用String,当字符串经常发生变化的时候使用StringBuffer:String 实际上都是常量,字符串的内容永远不会改变;StringBuffer可以为字符预留空间,因此是为经常变化的字符串考虑的
public class Test {   public static void stringReplace (String text) {   text = ('j' , 'i');    }      public static void bufferReplace (StringBuffer text) {   text = ("C");    }       public static void main (String args[]) {     String textString = new String ("java");     StringBuffer textBuffer = new StringBuffer ("java");         stringReplace (textString);     bufferReplace (textBuffer);         (textString + textBuffer);     }     }
public class E6 { public static void main(String args[]) {   String s1="a";  String s2=new String("a");  String s3="A";  ((s2));  ((s3));  ((s3)); }}
public class E6 { public static void main(String args[]) {   StringBuffer s1=new StringBuffer("a");  StringBuffer s2=new StringBuffer("a");  ((s2));   }}
public class E6 { public static void main(String args[]) {   String s1="a";  String s2="a";  String s3=new String("a");  String s4=new String("a");  (s1==s2);  (s3==s4);  (s1==s3);   } }
public class E6 { public static void main(String args[]) {   String s1="a";  StringBuffer sb1=new StringBuffer("a");    StringBuffer sb2=sb1;  String s2="a"+"b";  ("b");      (s1==s2);  (sb