java >> << .>>> 计算详解

通过一天的学习，整理了下面的小例子，分析了整数位运算的具体步骤，帮助大家理解和运用位运算符

package com.base;

public class Calculate {
    
    /**
     * 1 int 的取值是31位，最高位表示0表示正数，1表示负数
     *     min    = 10000000000000000000000000000000 = -2147483648
     *     max    = 01111111111111111111111111111111 =  2147483647
     * 2 负数使用补码表示，计算方法为最高位=1，其余31位为正数取反后加1
     *  20 = 00000000000000000000000000010100 
     *  取反  11111111111111111111111111101011
     *                                     +1
     * -20 = 11111111111111111111111111101100 
     * @param args
     */
    public static void main(String[] args) {
        
        //------- 整数位移运算---------------------------
        testLeft(2,16);// 正数左移
        testLeft(-2,16);//负数左移
        testRight(20,3);// 正数右移 
        testRight(-20,5);// 负数右移
        testUnsignedRight(20,5);// 正数无符号右移
        testUnsignedRight(-20,5);// 负数无符号右移
        //二进制取值范围
        testIntegerRag();  //int
    }

    

    /**
     *  2 << 16
     *         2 = 00000000000000000000000000000010 
     *      << 16
     *             00000000000000100000000000000000
     *      = 131072
     *  
     *  -2 << 16
     *      -2= 11111111111111111111111111111110
     *      << 16
     *          11111111111111100000000000000000
     *        = -131072
     */
    private static void testLeft(int i,int n) {
        System.out.println(" ---------- "+i+" << "+n+" -----------------");
        System.out.println("before = "+Integer.toBinaryString(i));
        int a = i << n;
        System.out.println(" after = "+Integer.toBinaryString(a));
        System.out.println("result = "+a);
    }
    
    /**
     * 4 >> 1   -- 0100 >> 0010  正数右移
     *                          负数右移
     * -20 >> 4  11111111111111111111111111101100 
     *   - >>4   1111111111111111111111111110 
     *   - -1    1111111111111111111111111101
     *   - 取反   1000000000000000000000000010 = -2 
     *   
     * -20 >> 5  11111111111111111111111111101100 
     *   - >>5   111111111111111111111111111 
     *   - -1    111111111111111111111111110
     *   - 取反   100000000000000000000000001 = -1   
     * @param i
     * @param n
     */
    private static void testRight(int i,int n) {
        System.out.println(" ---------- "+i+" >> "+n+" -----------------");
        System.out.println("before = "+Integer.toBinaryString(i));
        int a = i >> n;
        System.out.println(" after = "+Integer.toBinaryString(a));
        System.out.println("result = "+a);
    }
    
    /**
     * 无符号位置
     * -20 >>> 5
     *  -20    =  11111111111111111111111111101100
     * >>> 5   =  111111111111111111111111111
     * 转十进制 =  134217727
     *  20 >>> 5
     *   20    =  00000000000000000000000000010100
     * >>> 5   =  00000000000000000000000000000000
     * 转十进制 =  0
     * @param i
     * @param n
     */
    private static void testUnsignedRight(int i,int n){
        System.out.println(" ---------- "+i+" >>> "+n+" -----------------");
        System.out.println("before = "+Integer.toBinaryString(i));
        int a = i >>> n;
        System.out.println(" after = "+Integer.toBinaryString(a));
        System.out.println("result = "+a);
    }
    
    /**
     * Integer 二进制取值范围 
     */
    private static void testIntegerRag() {
        System.out.println(" ---------- int -----------------");
        System.out.println(" "+Integer.toBinaryString(Integer.MIN_VALUE)+"="+Integer.MIN_VALUE);
        System.out.println("  "+Integer.toBinaryString(Integer.MAX_VALUE)+"= "+Integer.MAX_VALUE);
    }
}