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()