public final class Stringimplements java.io.Serializable, Comparable<String>, CharSequence {/** The value is used for character storage. */private final char value[];/** Cache the hash code for the string */private int hash; // Default to 0public String() {this.value = new char[0];}public String(char value[]) {this.value = Arrays.copyOf(value, value.length);}
| 

    public static void main(String[] args){  String s0 = "adanac";  String s1 = "adanac";  String s2 = "ada" + "nac";  System.out.println(s0 == s1);       // true  System.out.println(s0 == s2);       // true  }

    public static void main(String[] args){  String s0 = "adanac";  String s1 = new String("adanac");  String s2 = "ada" + new String("nac");  System.out.println(s0 == s1);       // false  System.out.println(s0 == s2);       // false  System.out.println(s1 == s2);       // false  }

public class Test {public static void main(String srgs[]){ String str = "hello java!" ; String str1 = new String("hello java!") ;//str 和 str1 的区别在于：str 内存中有一个对象，而str1 内存中有两个对象。sop(str.length()) ;sop(str.charAt(i))  ; sop(str.indexOf('a')) ;sop(str.indexOf('a',7)) ;sop(str.indexOf("java")) ;sop(str.lastIndexOf('a')) ; }//打印函数：public static void sop(Object obj) {System.out.println(obj); }
}

public class Test{public static void main(String args[]){String str1 = "hello java!" ; String str2 = new String("hello java!") ;  System.out.println(str1.equals(str2));  //true [String类重写了Object类的equals 方法]System.out.println(str1 == str2);  //false}
}

public class Test {public static void main(String args[]){char[] ch = {'h','e' ,'l' ,'l' ,'o' ,' ' , 'j' , 'a' , 'v' ,'a'} ;// 构造函数转换：// 将字符数组转换成字符串：String str1 = new String (ch) ; System.out.println(str1);// 从ch[] 下标 6开始，后的4个字符 ，转换成字符串。String str2 = new String (ch,6,4) ;System.out.println(str2);//  静态方法：//  将字符数组转换成字符串：String str3 = String.copyValueOf(ch) ; System.out.println(str3); //  从ch[] 下标 6开始，后的4个字符 ，转换成字符串。String str4 = String.copyValueOf(ch,0,5) ;System.out.println(str4);String str = "hello java" ; // 将字符串转换成字符数组；char[] ch1 = str.toCharArray() ;for(int i = 0 ; i < ch1.length ; i ++)System.out.print("'"+ch1[i] +"'");System.out.println();   }
}

String str = "    hello,java,Adanac    " ; //替换字符
String str1 = str.replace(',', ' ') ;//切割
String[] str2 = str.split(",") ; // 除去字符串两端的多个空格：
System.out.println(str1.trim()); String str2 = "hello world " ;
//对比两个字符串进行自然顺序的比较
System.out.println(str.compareTo(str2));

class StringTest
{public static void sop(String str){System.out.println(str);}public static void main(String[] args) {String s = "      ab cd      ";sop("("+s+")");s = myTrim(s);sop("("+s+")");sop("("+reverseString(s)+")");}//练习二：将字符串反转。/*思路：1，将字符串变成数组。2，对数组反转。3，将数组变成字符串。*/public static String reverseString(String s,int start,int end){//字符串变数组。char[] chs = s.toCharArray();//反转数组。reverse(chs,start,end);//将数组变成字符串。return new String(chs);}public static String reverseString(String s){return reverseString(s,0,s.length());}private static void reverse(char[] arr,int x,int y){for(int start=x,end=y-1; start<end ; start++,end--){swap(arr,start,end);}}private static void swap(char[] arr,int x,int y){char temp = arr[x];arr[x] = arr[y];arr[y] = temp;}//练习一，去除字符串两端空格。/*思路：1，判断字符串第一个位置是否是空格，如果是继续向下判断，直到不是空格为止。结尾处判断空格也是如此。2，当开始和结尾都判断到不是空格时，就是要获取的字符串。*/public static String myTrim(String str){int start = 0,end = str.length()-1;while(start<=end && str.charAt(start)==' ')start++;while(start<=end && str.charAt(end)==' ')end--;return str.substring(start,end+1);}
}

class  StringTest
{/*练习三。获取一个字符串在另一个字符串中出现的次数。"abkkcdkkefkkskk"思路：1，定义个计数器。2，获取kk第一次出现的位置。3，从第一次出现位置后剩余的字符串中继续获取kk出现的位置。每获取一次就计数一次。4，当获取不到时，计数完成。*/public static int getSubCount(String str,String key){int count = 0;int index = 0;while((index=str.indexOf(key))!=-1){sop("str="+str);str = str.substring(index+key.length());count++;  }return count;}/*练习三，方式二。*/public static int getSubCount_2(String str,String key){int count = 0;int index = 0;while((index= str.indexOf(key,index))!=-1){sop("index="+index);index = index + key.length();count++;}return count;}public static void main(String[] args) {String str = "kkabkkcdkkefkks";///sop("count====="+str.split("kk").length);不建议使用。sop("count="+getSubCount_2(str,"kk"));}public static void sop(String str){System.out.println(str);}
}class  StringTest
{/*练习四。获取两个字符串中最大相同子串。第一个动作：将短的那个串进行长度一次递减的子串打印。"abcwerthelloyuiodef""cvhellobnm"思路：1，将短的那个子串按照长度递减的方式获取到。2，将每获取到的子串去长串中判断是否包含，如果包含，已经找到！。*/public static String getMaxSubString(String s1,String s2){String max = "",min = "";max = (s1.length()>s2.length())?s1: s2;min = (max==s1)?s2: s1;sop("max="+max+"...min="+min);for(int x=0; x<min.length(); x++){for(int y=0,z=min.length()-x; z!=min.length()+1; y++,z++){String temp = min.substring(y,z);sop(temp);if(max.contains(temp))//if(s1.indexOf(temp)!=-1)return temp;}}return "";}public static void main(String[] args) {String s1 = "ab";String s2 = "cvhellobnm";sop(getMaxSubString(s2,s1));}public static void sop(String str){System.out.println(str);}
}

public class StringBufferDemo
{public static void main(String[] args){  System.out.println("");DeleteString(new StringBuffer("hello java")) ;System.out.println("-------------------------------");ReplaceString(new StringBuffer("hello java")) ;}public static void CreateString(StringBuffer stringBuffer ){// 添加数据到stringBuffer 结尾处，stringBuffer.append("hello").append("java").append(520).append(true) ; System.out.println(stringBuffer);//在指定位置添加数据。stringBuffer.insert(0, "heima,"); System.out.println(stringBuffer);}public static void DeleteString(StringBuffer stringBuffer){ //删除start至end的字符序列。stringBuffer.delete(0,6);System.out.println(stringBuffer);//删除指定位置的字符stringBuffer.deleteCharAt(1) ;System.out.println(stringBuffer); }public static void ReplaceString(StringBuffer stringBuffer){//替换指定字符序列。stringBuffer.replace(6, stringBuffer.length(), "adanac") ; System.out.println(stringBuffer);stringBuffer.setCharAt(5, ',') ;System.out.println(stringBuffer);//反转stringBuffer.reverse(); System.out.println(stringBuffer); }
}