關於Java裡面的字串拼接，你了解多少？

string

text="我是攻城師1";

string text2=new

string("我是攻城師2")

//difference 1

string a = null;
string b = "foo";
string c = a + b; // c = nullfoo
string d = b.concat(a); // 空指標
string e = a.concat(b); // 空指標
//difference 2
string x = "1" + 2; // x = 12
string y = "1".concat(2); // 編譯錯誤

string c ="a" + "b";

c = new stringbuilder()

.tostring();

string c=」a「.concat("b")

public

string
concat(string
str) 
int len = value.length;
char buf = arrays.copyof(value, len + otherlen);
str.getchars(buf, len);
return
newstring(buf, true);
}

final

int loop_count=10000;
// 1 +
string s1="s1";
long starttime=system.nanotime();
for (int i = 0; i < loop_count; i++) 
long duration=system.nanotime()-starttime;
system.out.println(" + cost: "+duration/1000+" 微秒 ");
// 2 concat
string s2="s2";
starttime=system.nanotime();
for (int i = 0; i < loop_count; i++) 
duration=system.nanotime()-starttime;
system.out.println(" concat cost: "+duration/1000+" 微秒 ");
// 3 stringbuffer
stringbuffer s3=new stringbuffer("s3");
starttime=system.nanotime();
for (int i = 0; i < loop_count; i++) 
duration=system.nanotime()-starttime;
system.out.println(" stringbuffer cost: "+duration/1000+" 微秒 ");
// 4 stringbuilder
stringbuilder s4=new stringbuilder("s4");
starttime=system.nanotime();
for (int i = 0; i < loop_count; i++) 
duration=system.nanotime()-starttime;
system.out.println(" stringbuilder cost: "+duration/1000+" 微秒 ");

+ cos

t:432673
微秒  concat cos
t:49118
微秒  stringbuffer cos
t:1011
微秒  stringbuilder cos
t:734
微秒

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