java之数据类型输出

在java中，不可以直接声明超出int数据类型规定大小范围的数。例如int x=999999999999999999，这个是无法声明的，需要将其设置为long长整型，即long x=999999999999999l,尾缀为l表示为long型。同理，float类型声明也不可以直接声明为12.56，需要在末尾数字后面尾缀f，即 float c=21.34f，只有这样才可以声明。

Scanner cin=new Scanner(System.in);
        while(cin.hasNextDouble())//判断输入流中是否有双精度浮点数
        {
            double x=cin.nextDouble();
            sum=sum+x;
            n++;
        }

while的作用是循环输入数，判断条件是当输入的数据类型非数字时退出循环。

结果

"C:Program FilesJavajdk1.8.0_144binjava.exe" "-javaagent:C:Program FilesJetBrainsIntelliJ IDEA 2018.2.4libidea_rt.jar=55154:C:Program FilesJetBrainsIntelliJ IDEA 2018.2.4bin" -Dfile.encoding=UTF-8 -classpath "C:Program FilesJavajdk1.8.0_144jrelibcharsets.jar;C:Program FilesJavajdk1.8.0_144jrelibdeploy.jar;C:Program FilesJavajdk1.8.0_144jrelibextaccess-bridge-64.jar;C:Program FilesJavajdk1.8.0_144jrelibextcldrdata.jar;C:Program FilesJavajdk1.8.0_144jrelibextdnsns.jar;C:Program FilesJavajdk1.8.0_144jrelibextjaccess.jar;C:Program FilesJavajdk1.8.0_144jrelibextjfxrt.jar;C:Program FilesJavajdk1.8.0_144jrelibextlocaledata.jar;C:Program FilesJavajdk1.8.0_144jrelibextnashorn.jar;C:Program FilesJavajdk1.8.0_144jrelibextsunec.jar;C:Program FilesJavajdk1.8.0_144jrelibextsunjce_provider.jar;C:Program FilesJavajdk1.8.0_144jrelibextsunmscapi.jar;C:Program FilesJavajdk1.8.0_144jrelibextsunpkcs11.jar;C:Program FilesJavajdk1.8.0_144jrelibextzipfs.jar;C:Program FilesJavajdk1.8.0_144jrelibjavaws.jar;C:Program FilesJavajdk1.8.0_144jrelibjce.jar;C:Program FilesJavajdk1.8.0_144jrelibjfr.jar;C:Program FilesJavajdk1.8.0_144jrelibjfxswt.jar;C:Program FilesJavajdk1.8.0_144jrelibjsse.jar;C:Program FilesJavajdk1.8.0_144jrelibmanagement-agent.jar;C:Program FilesJavajdk1.8.0_144jrelibplugin.jar;C:Program FilesJavajdk1.8.0_144jrelibresources.jar;C:Program FilesJavajdk1.8.0_144jrelibrt.jar;G:ee程序L1outproductionL1" com.company.Main
请输多个数，最后输入enter建或者空格键结束
最后输入一个非数字结束符
1
2
3
2.3
4.56
f
共输入了5个数，其和为：12.86

进程完成，退出码 0

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