Java中String的常用方法

开发中涉及到大量的对String的处理，熟练掌握String的常用方法,可以提高开发效率。

1. 字符与字符串，常用的方法有:

• public String(char[] value)
• public String(char[] value, int offset, int count)
• public char charAt(int index)
• public char[] toCharArray()

{
    //public char charAt(int index)
    //取出指定索引的字符
    String str = "hello";
    char c = str.charAt(1);
    System.out.println(c);
}

{
    //public char[] toCharArray()
    //字符数组与字符串的转换 
    String str = "hello";
    char[] strInCharArray = str.toCharArray();
    for(char item : strInCharArray)
    {
        System.out.print(item + " ");
    }
    System.out.println();
}

{
    //public char[] toCharArray()
    //判断一个给定的字符串是否有数字组成
    String str = "13212A355565";
    char[] strInCharArray = str.toCharArray();
    boolean flag = true;
    for(char item : strInCharArray)
    {
        if(item < '0' || item > '9')
        {
            flag = false;
            break;
        }
    }
    
    System.out.print(str + ": ");
    if(flag)
    {
        System.out.println("全部由数字组成!");
    }
    else
    {
        System.out.println("不是全由数字组成!");
    }
}

2.　字节与字符串

• String(byte[] bytes)
• String(byte[] bytes, int offset, int length)
• public byte[] getBytes()
• public byte[] getBytes(Charset charset)

//public byte[] getBytes()
//字符串与字节数组的转换
String str = "hello world";
byte[] strInBytes = str.getBytes();
for(byte item : strInBytes)
{
    System.out.println((int)item);
}

3. 字符串比较

• public boolean equals(Object anObject)
• public boolean equalsIgnoreCase(String anotherString)

String str1 = "hello";
String str2 = "HELLO";

System.out.println(str1.equals(str2));//false
System.out.println(str1.equalsIgnoreCase(str2));//true

4. 字符串查找

• public boolean contains(CharSequence s)
• public int indexOf(String str)
• public int indexOf(String str, int fromIndex)
• public int lastIndexOf(String str)
• public int lastIndexOf(String str, int fromIndex)
• boolean startsWith(String prefix)
• public boolean startsWith(String prefix, int toffset)
• public boolean endsWith(String suffix)

String str = "hello world";
System.out.println(str.indexOf("world"));
System.out.println(str.indexOf("l"));
System.out.println(str.indexOf("l",5));
System.out.println(str.lastIndexOf("l"));

 5. 字符串替换

• public String replaceAll(String regex, String replacement)
• public String replaceFirst(String regex, String replacement)

String str = "hello world";
String resultA = str.replaceAll("l", "*");
String resultB = str.replaceFirst("l", "*");
System.out.println(str);
System.out.println(resultA);
System.out.println(resultB);

6. 字符串截取

• public String substring(int beginIndex)
• public String substring(int beginIndex,int endIndex)

String str="hello world";
String resultA = str.substring(6);
String resultB = str.substring(2, 4);
System.out.println(resultA);
System.out.println(resultB);

7. 字符串拆分

• public String[] split(String regex)
• public String[] split(String regex, int limit)

String str="192.168.1.1";
String[] results = str.split("\.");
for(String item : results)
{
    System.out.print(item+" ");
}

8. 其它常用方法

• public String toLowerCase()
• public String toUpperCase()
• public String trim()
• public String concat(String str)
• public int length()
• public boolean isEmpty()