stringbuilder - java StringBuilding 定义

Question

这2种定义方式 有不同吗??
第一种会慢吗?

Answer 1

Answer: Just as fast

String initialization operation:

String s= "a"+"b";
String s1= "ab";

This way the compiler is the same by default. So it won’t be slow

Another example:

  String a= "a";
  String b = "b";
  String s2= a+b;

The s2 produced like this is very slow because the memory is requested three times.

I hope you will adopt it and give me points if you are satisfied. . I am a new member and hope to serve you all! ! ! (I really want to give -1 point to the first answer, just give it a few random answers)

Answer 2

The first type is not just a slow problem, but a code that looks like shit.

new StringBuilder("a").append("b").append("c");

---

new StringBuilder("a" + "b" + "c");

If you use it like the above, it is better to directly use "a" + "b" + "c"因为没有使用到StringBuilder的任何特性，加上JDK’s compilation and optimization. The final code will become as follows.

new StringBuilder(new StringBuilder("a").append("b").append("c").toString());

I don’t understand the second one at all. What is the meaning of using StringBuilder? Isn't it just a string in itself?

Answer 3

javap -c看看，编译器应该会把你用+The connected string constants are spliced ​​together, and the two writing methods should run the same.

Answer 4

Constants can be used directly +
Variables can also be used +
If you care about performance, check this out: http://calvin1978.blogcn.com/...

Answer 5

As long as the splicing character '+' is not used between objects, there is basically no difference between using the splicing character '+' between strings and not using it; and once the string object is generated, it will be modified to generate another object with all strings Splicing between objects will be very slow;

public static void main(String[] args) {

fun1(10000000);

}
private static void fun1(int length){

long min1 = new Date().getTime();
System.out.println(min1);
//1
for(int i=0;i<length;i++){
    new StringBuffer("字符1;" +
            "字符2;" +
            "字符3;" +
            "字符4;" +
            "字符5;");
}
long min2 = new Date().getTime();
System.out.println(min2);
System.out.println(min2-min1);

}
private static void fun2(int length){

long min1 = new Date().getTime();
System.out.println(min1);
//2
for(int i=0;i<length;i++){
    new StringBuffer("字符1;字符2;字符3;字符4;字符5;");
}
long min2 = new Date().getTime();
System.out.println(min2);
System.out.println(min2-min1);

}
private static void fun3(int length){

long min1 = new Date().getTime();
System.out.println(min1);
//3
for(int i=0;i<length;i++){
    String aa = "字符1;" +
    "字符2;" +
    "字符3;" +
    "字符4;" +
    "字符5;";
    new StringBuffer(aa);
}
long min2 = new Date().getTime();
System.out.println(min2);
System.out.println(min2-min1);

}
private static void fun4(int length){

long min1 = new Date().getTime();
System.out.println(min1);
//3
for(int i=0;i<length;i++){
    String aa = "字符1;" ;
    aa +="字符2;" ;
    aa +="字符3;" ;
    aa +="字符4;" ;
    aa +="字符5;";
    new StringBuffer(aa);
}
long min2 = new Date().getTime();
System.out.println(min2);
System.out.println(min2-min1);

}

Answer 6

These two methods of creating objects are faster and slower. In fact, they can be converted into the following two methods to compare faster and slower:

String a = "Test";
String b = "T" + "e" + "s" + "t";

Of course these two methods are equally fast. In the JVM, "T" + "e" + "s" + "t" are actually processed as "Test".
Let’s now take a look at the following string splicing method:

String a = "Te";
String b = a + "st";

The above method is the least efficient method of string splicing and is extremely not recommended, because when this kind of string splicing is done, the JVM actually generates a new StringBuilder, then calls the append method, and then performs toString. The speed is simply It’s a slow dog (dog: I’m lying on the gun again...)
So to sum up: the two new StringBuilder methods written by the subject are actually the same method, the efficiency is the same, and they are straightforward.