JAVA易错点详解(数据类型转换、字符串与运算符)

byte a = 10;
byte b = 20;
byte c = (byte)(a+b);//byte型的a与b参与计算后变为8个字节
      //byte型的c只能有一个字节，所以发生了强制类型转换
System.out.println(c);//30

String str = "abcd";
或者
String str;
str = "abcd";

int a = 10;
int b = 20;
System.out.println("a = "+a +"b = "+b);//a = 10b = 20
System.out.println(a+b);

System.out.println("a + b = "+a+b);//a + b = 1020
System.out.println(a+b+"a + b ");//30a + b 

System.out.println(10%0);//编译错误
        System.out.println(11.5%5);//1.5
        System.out.println(10/-2);//-5
        System.out.println(-10/2);//-5
        System.out.println(-10/-2);//5

int a  =10;
        a =a++;
        System.out.println(a);//输出结果为10

int a  = 4;
      double d = 5.0;
      a += d;
        //+=操作符来说,会自动转换
      System.out.println(a);

int a = 10;
System.out.println(!a);//错误
System.out.println(!false);
System.out.println(!true);