/** String的属性值 */  
    private final char value[];

    /** The offset is the first index of the storage that is used. */
    /**数组被使用的开始位置**/
    private final int offset;

    /** The count is the number of characters in the String. */
    /**String中元素的个数**/
    private final int count;

    /** Cache the hash code for the string */
   /**String类型的hash值**/
    private int hash; // Default to 0

    /** use serialVersionUID from JDK 1.0.2 for interoperability */
    private static final long serialVersionUID = -6849794470754667710L;
    /**
     * Class String is special cased within the Serialization Stream         Protocol.
     *
     * A String instance is written into an ObjectOutputStream according to
     * <a href="{@docRoot}/../platform/serialization/spec/output.html">
     * Object Serialization Specification, Section 6.2, "Stream Elements"</a>
     */

　　private static final ObjectStreamField[] serialPersistentFields =
        new ObjectStreamField[0];

public class TestString {
    public static void main(String[] args) {
           // 创建字符串对象
        String s1 = "hello";
        String s2 = "hello";
        String s3 = "Hello";
 
        // boolean equals(Object obj):比较字符串的内容是否相同
        System.out.println(s1.equals(s2));
        System.out.println(s1.equals(s3));
        System.out.println("-----------");
 
        // boolean equalsIgnoreCase(String str):比较字符串的内容是否相同,忽略大小写
        System.out.println(s1.equalsIgnoreCase(s2));
        System.out.println(s1.equalsIgnoreCase(s3));
        System.out.println("-----------");
 
        // boolean startsWith(String str):判断字符串对象是否以指定的str开头
        System.out.println(s1.startsWith("he"));
        System.out.println(s1.startsWith("ll"));
    }

}

public class TestString {
    public static void main(String[] args) {
        String str1 = "Lance";
        String str2 = new String("Lance");
        String str3 = "LANCE";
        
        // boolean equals(Object obj):比较字符串的内容是否相同
        System.out.println(str1.equals(str2));
        System.out.println(str1.equals(str3));
        System.out.println("-----------------------");
        
        // boolean equalsIgnoreCase(String str):比较字符串的内容是否相同,忽略大小写
        System.out.println(str1.equalsIgnoreCase(str3));
        System.out.println("-----------------------");
        
        // boolean startsWith(String str):判断字符串对象是否以指定的str开头
        // boolean endsWith(String str): 判断字符串对象是否以指定的str结尾
        System.out.println(str1.startsWith("La"));
        System.out.println(str3.endsWith("CE"));
        
    }

}
　　结果：

　　　　

3.2、String类的获取功能

　　1）常用方法

 int length():获取字符串的长度，其实也就是字符个数
 char charAt(int index):获取指定索引处的字符
 int indexOf(String str):获取str在字符串对象中第一次出现的索引
 String substring(int start):从start开始截取字符串
 String substring(int start,int end):从start开始，到end结束截取字符串。包括start，不包括end
　　2）测试代码

public class TestString {
    public static void main(String[] args) {
          // 创建字符串对象
        String s = "helloworld";
 
        // int length():获取字符串的长度，其实也就是字符个数
        System.out.println(s.length());
        System.out.println("--------");
 
        // char charAt(int index):获取指定索引处的字符
        System.out.println(s.charAt(0));
        System.out.println(s.charAt(1));
        System.out.println("--------");
 
        // int indexOf(String str):获取str在字符串对象中第一次出现的索引
        System.out.println(s.indexOf("l"));
        System.out.println(s.indexOf("owo"));
        System.out.println(s.indexOf("ak"));
        System.out.println("--------");
 
        // String substring(int start):从start开始截取字符串
        System.out.println(s.substring(0));
        System.out.println(s.substring(5));
        System.out.println("--------");
 
        // String substring(int start,int end):从start开始，到end结束截取字符串
        System.out.println(s.substring(0, s.length()));
        System.out.println(s.substring(3, 8));
        
    }

}

public class TestString {
    public static void main(String[] args) {
         // 创建字符串对象
        String s = "abcde";
 
        // char[] toCharArray():把字符串转换为字符数组
        char[] chs = s.toCharArray();
        for (int x = 0; x < chs.length; x++) {
            System.out.println(chs[x]);
        }
 
        System.out.println("-----------");
 
        // String toLowerCase():把字符串转换为小写字符串
        System.out.println("HelloWorld".toLowerCase());
        // String toUpperCase():把字符串转换为大写字符串
        System.out.println("HelloWorld".toUpperCase());
        
    }

}

public class TestString {
    public static void main(String[] args) {
          // 创建字符串对象
        String s1 = "helloworld";
        String s2 = " helloworld ";
        String s3 = " hello world ";
        System.out.println("---" + s1 + "---");
        System.out.println("---" + s1.trim() + "---");
        System.out.println("---" + s2 + "---");
        System.out.println("---" + s2.trim() + "---");
        System.out.println("---" + s3 + "---");
        System.out.println("---" + s3.trim() + "---");
        System.out.println("-------------------");
 
        // String[] split(String str)
        // 创建字符串对象
        String s4 = "aa,bb,cc";
        String[] strArray = s4.split(",");
        for (int x = 0; x < strArray.length; x++) {
            System.out.println(strArray[x]);
        }
    }

}