Java基础-基本数据类型之间的转换

3+'A'+45L
5+3.6+ 'A'+3.14f

package com.cwl.base.day01;

/**
 * @program: java_base
 * @description: 测试基本数据类型(整型变量)
 * @author: ChenWenLong
 * @create: 2019-11-05 15:11
 **/
public class TestPrimitiveDataType {

    public static void main(String[] args) {
        //测试整型变量
        int  a = 15;
        int  b = 015;	//以0开头是八进制
        int  c = 0x15;	//以0x开头是16进制
        int  d = 0b1101;	//以0b开头是二进制

        System.out.println(b);
        System.out.println(c);
        System.out.println(d);

        byte  age = 30;
        short  salary = 30000;
        int   population = 2000000000;			//整型常量默认是int类型
        long  globalPopulation = 7400000000L;	//后面加L就是这是一个long类型的常量


    }
}

package com.cwl.base.day01;

import java.math.BigDecimal;

/**
 * @program: java_base
 * @description: 测试浮点型
 * @author: ChenWenLong
 * @create: 2019-11-05 15:13
 **/
public class TestPrimitiveDataType2 {

    public static void main(String[] args) {
        float a = 3.14F;
        double b = 6.28;
        double c = 628E-2;

        System.out.println(c);

        // 浮点数是不精确的，一定不要用于比较！
        float f = 0.1f;
        double d = 1.0 / 10;
        System.out.println(f == d); // 结果为false

        float d1 = 423432423f;
        float d2 = d1 + 1;
        if (d1 == d2) {
            System.out.println("d1==d2");// 输出结果为d1==d2
        } else {
            System.out.println("d1!=d2");
        }

        System.out.println("##################");
        //使用精确浮点运行，推荐：BigDecimal
        BigDecimal bd = BigDecimal.valueOf(1.0);
        bd = bd.subtract(BigDecimal.valueOf(0.1));
        bd = bd.subtract(BigDecimal.valueOf(0.1));
        bd = bd.subtract(BigDecimal.valueOf(0.1));
        bd = bd.subtract(BigDecimal.valueOf(0.1));
        bd = bd.subtract(BigDecimal.valueOf(0.1));
        System.out.println(bd);// 0.5
        System.out.println(1.0 - 0.1 - 0.1 - 0.1 - 0.1 - 0.1);// 0.5000000000000001

        BigDecimal  bd2 = BigDecimal.valueOf(0.1);
        BigDecimal  bd3 = BigDecimal.valueOf(1.0/10.0);

        System.out.println(bd2.equals(bd3));

    }
}

package com.cwl.base.day01;

/**
 * @program: java_base
 * @description: 测试字符类型和布尔类型
 * @author: ChenWenLong
 * @create: 2019-11-05 15:14
 **/
public class TestPrimitiveDataType3 {

    public static void main(String[] args) {
        char  a = 'T';
        char  b = '尚';
        char c = '\u0061';
        System.out.println(c);

        //转义字符
        System.out.println(""+'a'+'\n'+'b');
        System.out.println(""+'a'+'\t'+'b');
        System.out.println(""+'a'+'\''+'b');		//a'b


        //String就是字符序列
        String  d = "abc";

        //测试布尔类型
        boolean  man = false;

        if(man){		//极端不推荐：man==true
            System.out.println("男性");
        }

    }
}

package com.cwl.base.day01;

/**
 * @program: java_base
 * @description: 测试自动类型转化
 * @author: ChenWenLong
 * @create: 2019-11-05 15:17
 **/
public class TestTypeConvert {

    public static void main(String[] args) {
        int  a = 324;
        long  b = a;
        double  d = b;
//		a = b;
//		long  e = 3.23F;
        float  f = 234324L;

        //特例
        byte  b2 = 123;

    }
}

package com.cwl.base.day01;

/**
 * @program: java_base
 * @description: 测试类型转换常见问题
 * @author: ChenWenLong
 * @create: 2019-11-05 15:18
 **/
public class TestTypeConvertError {

    public static void main(String[] args) {
        int money = 1000000000; //10亿
        int years = 20;
        //返回的total是负数，超过了int的范围
        int total = money*years;
        System.out.println("total="+total);
        //返回的total仍然是负数。默认是int，因此结果会转成int值，再转成long。但是已经发生//了数据丢失
        long total1 = money*years;
        System.out.println("total1="+total1);
        //返回的total2正确:先将一个因子变成long，整个表达式发生提升。全部用long来计算。
        long total2 = money*((long)years);
        System.out.println("total2="+total2);

        long   total3 = 34L*3223*years*223423;
        System.out.println(total3);
        //命名问题
        int l = 2; //分不清是L还是1,
        long a = 23451l;//建议使用大写L
        System.out.println(l+1);

    }
}