Java Day 15

String
 字符串对象一旦被初始化就不会被改变
 
 字符串常量池
 
 String s = "abc"; //字符串常量池
 String s = new String("abc");//在堆内存中
 字符串== 比较地址值
 String类中的equals复写了Object，比较字符串内容
 
String构造函数

常见方法
 获取
 转换 字符串切割
  split
  trim
 判断
 比较
 intern方法 对字符串池进行操作

字符串数组排序
获取字符串次数

    private static int getStringcounts(String ss, String key) {
        int counts = 0;
        int index = 0;
        while((index=ss.indexOf(key))!= -1){
            index += key.length();
            ss = ss.substring(index);
            counts++;
        }
        return counts;
    }

查找最大子字符串

    public static String maxSubString(String s1,String s2){
        String max = null;
        String min = null;
        max=(s1.length()>s2.length())?s1:s2;
        min=(max.equals(s1))?s2:s1;

        for (int i = 0; i <min.length() ; i++) {
            for (int j =0,k=min.length()-i;k!=min.length()+1;j++,k++) {
                String sub = min.substring(j,k);
                if(max.contains(sub))
                    return sub;
            }
        }
        return null;
    }

去除两端空白 模拟trim()

    private static String getStringTrim(String s1) {
        int start = 0,end = s1.length()-1;
        while(start<=end && ' ' == s1.charAt(start)){
            start++;
        }
        while(start<=end && ' ' == s1.charAt(end)){
            end--;
        }
        return s1.substring(start,end+1);
    }

StringBuffer
 append insert
 添加、删除、查找、修改
 //清空缓冲区
 sb.delete(0.sb.lenght())
 sb = new StringBuffer();

 setLength();
 
StringBuilder
 单线程，提高效率，不安全