public class TestString {    public static void main(String[] agrs){        String s1 = "hello";        String s2 = "Word";        String s3 = "hello";        System.out.PRintln(s1 == s3);               //因?yàn)閟1和s3并不是被new出來(lái)的        s1 = new String("hello");        s2 = new String("hello");        System.out.println(s1 == s2);        System.out.println(s1.equals(s2));        //雖然是new出來(lái)的，但是String類(lèi)對(duì)equals進(jìn)行了重寫(xiě)        char c[] = {'s','u','n',' ','j','a','v','a'};        String s4 = new String(c);        String s5 = new String(c,4,4);        System.out.println(s4);        System.out.println(s5);    }}結(jié)果是：?truefalsetruesun javajava?equals的API：Compares this string to the specified object. The result is true if and only if the argument is not null and is a String object that represents the same sequence of characters as this object.比較這個(gè)字符串到指定的對(duì)象。如果該參數(shù)不為空，是一個(gè)字符串對(duì)象表示相同的字符序列作為該對(duì)象的結(jié)果是真的。??2.String類(lèi)常用方法public char charAt(int index)                                           返回字符串中第index個(gè)字符?public int length ()                                                             返回字符串的長(zhǎng)度?public int indexOf(string str)                                            返回字符串中出現(xiàn)str的第一個(gè)位置?public int indexOf(string str,int fromIndex)                    返回字符串中從fromIndex開(kāi)始出現(xiàn)str的第一個(gè)位置?public int lastIndexOf(int ch)                                           查看ch字符最后出現(xiàn)的位置?public int lastIndexOf(String str)                                     字符串public boolean equalsIgnoreCase(string another)    比較字符串與another是否一樣（忽略大小寫(xiě)）?public String replace(char oldChar,char newChar)   在字符串中用newChar字符替換oldChar字符??舉例：
public class TestString {    public static void main(String[] agrs) {        String s1 = "sun java", s2 = "sun Java";        System.out.println(s1.charAt(1));        System.out.println(s1.length());        System.out.println(s1.indexOf("java"));        System.out.println(s1.indexOf("Java"));        System.out.println(s1.equals(s2));        System.out.println(s1.equalsIgnoreCase(s2));        String s = "我是程序員，我在學(xué)java";        String sr = s.replace('我', '你');        System.out.println(sr);    }}
結(jié)果是：
u   
8   
4  
-1  
 false  
true     
你是程序員，你在學(xué)java?
public boolean starsWith(String prefix)                         判斷字符串是否以prefix字符串開(kāi)頭?public boolean endsWith(String suffix)                         判斷字符串是否以suffix字符串解圍?public String toUpperCase()                                           返回一個(gè)字符串為該字符的大寫(xiě)形式?public String toLowerCase()                                           返回一個(gè)字符串為該字符的小寫(xiě)形式?public String substring(int beginIndex)                         返回該字符串從beginIndex開(kāi)始到結(jié)尾的子字符串?public String substring(int beginIndex,int endIndex)  返回該字符串從beginIndex開(kāi)始到endIndex結(jié)尾的字符串?Public String trim()                                                             返回將該字符串去掉開(kāi)頭和結(jié)尾空格后的字符串?public String[] split (String regex,int limit)                      將字符串分割成子字符串，返回字符串?dāng)?shù)組public byte[] getBytes()                                                     將該字符串轉(zhuǎn)換成byte數(shù)組?舉例：?
public class TestString {    public static void main(String[] agrs) {        String s = "Welcome to Java World!";        String s1 = " sun java ";        System.out.println(s.startsWith("Welcome"));        System.out.println(s.startsWith("World"));        String sL = s.toLowerCase();        String sU = s.toUpperCase();        System.out.println(sL);        System.out.println(sU);        String subS = s.substring(11);        System.out.println(subS);        String sp = s1.trim();        System.out.println(sp);    }}
結(jié)果是：
true
false
welcome to java world!WELCOME TO JAVA WORLD!Java World!sun java?3.常用方法(2)?靜態(tài)重載方法?public static String valueOf()         可以將基本類(lèi)型數(shù)據(jù)轉(zhuǎn)換為字符串；?例如：public static String valueOf(double d)?方法
public String[] split(String regex)  可以將一個(gè)字符串按照指定的分隔符分隔，返回分隔后的字符串?dāng)?shù)組。?
public class TestString {    public static void main(String[] agrs) {        int j = 1234567;        String sNumber = String.valueOf(j);        System.out.println("j是" + sNumber.length() + "位數(shù)");        String s = "Mary,F,1976";        String[] sPlit = s.split(",");        for (int i = 0; i < sPlit.length; i++) {            System.out.print(sPlit[i] + " ");        }    }}結(jié)果是：j是7位數(shù)Mary F 1976?統(tǒng)計(jì)字符串中大小寫(xiě)字母以及其他字符個(gè)數(shù)的程序：
public class TestString {    public static void main(String[] agrs) {        int lCount = 0, uCount = 0, oCount = 0;        String s = "advrsv^&jgjebjahvVHGFHBJHF^&*&fhaawd";        for (int i = 0; i < s.length(); i++) {            char c = s.charAt(i);            if (Character.isLowerCase(c)) {                lCount++;            } else if (Character.isUpperCase(c)) {                uCount++;            } else {                oCount++;            }        }        System.out.println("小寫(xiě)字母一共："+lCount + "個(gè)，大寫(xiě)字母一共：" + uCount + "個(gè),其他字符一共：" + oCount+"個(gè)");    }}
結(jié)果是：
小寫(xiě)字母一共：21個(gè)，大寫(xiě)字母一共：9ge,其他字符一共：6個(gè)
輸出一個(gè)字符串中部分字符段個(gè)數(shù)的程序：
public class TestString {    public static void main(String[] agrs) {        String s = "sunjavajijavahpjavaokjavawljavahuijavavbjava";        int count = 0;        String sToFind = "java";        int index = s.indexOf(sToFind);        if (index != -1) {            count++;        }        s = s.substring(index + sToFind.length());        while (s.indexOf(sToFind) != -1) {            index = s.indexOf(sToFind);            s = s.substring(index + sToFind.length());            count++;        }        System.out.println(count);    }}結(jié)果是：7?優(yōu)化程序：?
public class TestString {    public static void main(String[] agrs){        String s = "sunjavajijavahpjavaokjavawljavahuijavavbjava";        int count = 0;        String sToFind = "java";        int index = -1;        while((index = s.indexOf(sToFind)) != -1){          //給index賦值            s = s.substring(index + sToFind.length());            count++;        }        System.out.println(count);    }}