string in Java with []byte byte array

One, the string

1. + = overloaded Symbols and concat

STR1 + = str2: Lower- level StringBuilder are more efficient, but less flexible, and in some cases less efficient .

str1 = new StringBuilder (). Append (str1). Append (str2). toString ();

Concat: Returns a new string that is slightly more efficient when the string is small .

StringBuilder: Use append stitching, high efficiency in multi-segment string stitching .

@org. junit.testpublic void Test () {    int times = 100000;    String S1 = "";    String s2 = "";    StringBuilder s3 = new StringBuilder ("");    Long a = System.currenttimemillis ();    for (int i = 0; I < times; i + +) {        S1 + = "a";    }    Long B = System.currenttimemillis ();    for (int i = 0; I < times; i + +) {        s2 = s2.concat ("a");    }    Long C = System.currenttimemillis ();    for (int i = 0; I < times; i + +) {        s3.append ("a");    }    Long d = System.currenttimemillis ();    System.out.print ((b-a) + "|" + (C-B) + "|" + (D-C));}

Output results

7289 | 1593 | 5

2. Compare contains methods in String, HashSet, List

The IndexOf method is used by String and List, which is essentially traversal, and the time efficiency is O (n). The HashSet uses the method of calculating the hash value, the time efficiency is O (1) level.

Why do I need hashcode method in 3.String?

From the string source can see its underlying implementation is char[], that is, the essence is a character array. Both the index and most of the feature implementations use arrays.

Public final class String implements XXX  {        private final char value[];    /** Cache The hash code for the string */    private int hash;//Default to 0 public    string () {        this.value = "". value;    }    public string (string original) {        this.value = Original.value;        This.hash = Original.hash;    }

Why do we need hash values? The reason is that String acts as a key to the HashSet, HashMap container, so you need to get the value of the key's system.

string in Java with []byte byte array