Java-String.valueOf conversion and, empty string + type variableconversion and encapsulation class (Integer) way to convert the toStringcomparison.

 

1, an empty string + type variable way to convert

 

  

int i=20; 
String s=""+i;

 

 

this way actually been two steps, first carried out i.ToString () to i converted to a string, and then the addition operation, where the use of java toString mechanism to prevent conversion.

 

2, String.valueOf way to convert type

 

  

int i=20; 
String s=String.valueOf(i);

 

 

View source code found in this way is actually to use the wrapper classes (Integer) the toString way to convert.

 

  

1 public static String valueOf(int i) { 
2    return Integer.toString(i); 
3 }

 

 

 

3, using the type wrapper class's toString () method

 

 

  

Integer i=20; 
String s=i.toString();

 

 

view java source found, toString actually new a String.

 

simply the speed of the test.

 

 

  

public class toStringDome { 
    public static void main(String[] args) 
    { 
        Random ra=new Random(new java.util.Date().getTime()); 
        String tmp=null; 
        int runtimes=1000000; 
        int range=50; 
 
        long startTime=System.currentTimeMillis();   //获取开始时间 
        for (int i = 0; i <runtimes; i++) { 
            tmp=String.valueOf(ra.nextInt(range)); 
        } 
        long endTime=System.currentTimeMillis(); //获取结束时间 
 
        System.out.println("使用String.valueOf程序运行时间： "+(endTime-startTime)+"ms"); 
 
        long startTimeToString=System.currentTimeMillis();   //获取开始时间 
        for (int i = 0; i <runtimes; i++) { 
            tmp = ""+ra.nextInt(range); 
        } 
        long endTimeString=System.currentTimeMillis(); //获取结束时间 
        System.out.println("使用（空串来转换+类型变量）程序运行时间： "+(endTimeString-startTimeToString)+"ms"); 
 
 
        Integer temp=0; 
        long startTimeToString1=System.currentTimeMillis();   //获取开始时间 
        for (int i = 0; i <runtimes; i++) { 
            temp= ra.nextInt(range); 
            tmp =temp.toString(); 
        } 
        long endTimeString2=System.currentTimeMillis(); //获取结束时间 
 
        System.out.println("使用Integer的toString程序运行时间： "+(endTimeString2-startTimeToString1)+"ms"); 
 
 
    } 
}

运行结果：

  

Use String.valueOf run time: 87ms
use (the empty string to convert + type variable) running time: 245ms
use the toString Integer Program running time: 77ms

  

 

 

 

After a simple test and found, use (the empty string to convert + type variable) mode conversion ratio String.valueOf with Integer's toString slower than twice.

 

what I understand to use (the empty string to convert + type variable) mode conversion efficiency is slow because in this way actually been two steps, first carried out i.ToString () to convert i to a string, and then the string adder, because strings are immutable, are going to need new memory space to store a new string, the string adder affect the efficiency.