Java中加减乘除的性能和位运算的性能比较

public class TestDemo {
    int anInt = Integer.MAX_VALUE;

    //21亿次+
    public void funAdd() {
        long i1=System.currentTimeMillis();
        int sum=0;
        for(int i = 0; i< anInt; i++) {
            sum+=i;
        }
        System.out.println(anInt+"次+:"+(System.currentTimeMillis()-i1));
    }

    //21十亿次-
    public void funSubtract() {
        long i1=System.currentTimeMillis();
        int sum=0;
        for(int i = 0; i< anInt; i++) {
            sum-=i;
        }
        System.out.println(anInt+"次-:"+(System.currentTimeMillis()-i1));
    }

    //21亿次*
    public void funMultiply() {
        long i1=System.currentTimeMillis();
        int sum=1;
        for(int i=0;i
            sum*=2;
        }
        System.out.println(anInt+"次*:"+(System.currentTimeMillis()-i1));
    }

    //21亿次/
    public void funDivide() {
        long i1=System.currentTimeMillis();
        int sum=Integer.MAX_VALUE;
        for(int i=2;i
            sum/=2;
        }
        System.out.println(anInt+"次/:"+(System.currentTimeMillis()-i1));
    }

    //21亿次<<1 等效*2
    public void funMultiplyBit() {
        long i1=System.currentTimeMillis();
        int sum=1;
        for(long i = 0; i< anInt; i++) {
            sum= sum << 1;
        }
        System.out.println(anInt+"次位乘2:"+(System.currentTimeMillis()-i1));
    }

    //21亿次>>1 等效/2
    public void funDivideBit() {
        long i1=System.currentTimeMillis();
        int sum=Integer.MAX_VALUE;
        for(long i = 0; i< anInt; i++) {
            sum=sum>>1;
        }
        System.out.println(anInt+"次位除2:"+(System.currentTimeMillis()-i1));
    }

    public static void main(String[] args) {
        TestDemo demo = new TestDemo();
        demo.funAdd();
        demo.funSubtract();
        demo.funMultiply();
        demo.funDivide();
        demo.funMultiply();
        demo.funDivideBit();
        }
    }

在运算中，优先使用 【>> 1】 来代替 【/ 2】可大大提升程序性能