java性能问题

Question

public class Guava implements Runnable {
public static void main(String []a){
new Thread(new Guava()).start();
}
@Override
public void run() {
long end;
long start;
int temp=0;
while(true){

    start=System.currentTimeMillis();   
    for(int i=0;i<1000000000;i++){
        int b=0;
        temp=++b;
    }
    end=System.currentTimeMillis();
    System.out.println("1:"+(end-start));
    System.out.println("b="+temp);
    //---------------------------------------
    start=System.currentTimeMillis();
    int c=0;
    for(int j=0;j<1000000000;j++){
        c=0;
        temp=++c;
    }
    end=System.currentTimeMillis();
    System.out.println("2:"+(end-start));
    System.out.println("c="+temp);
    //---------------------------------------
    try {
        new Thread().sleep(3000);
    } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    System.out.println("---------------------------------------");}
}
}
![图片说明](https://img-ask.csdn.net/upload/201603/24/1458785966_300029.png)

为什么 case1 比较快

Answer 1

用内存空间换取时间。