package com.yuque.phil616.datatype;
public class DataType {
    public static void main(String[] args) {
        /**
         * **********CHAPTER ONE*************
         * there are eight basic datatype in java.
         * they are
         * byte short int long boolean char
         * double float
         * and when the basic data type variable have been declared
         * each variable will be assignment a default value.
         * following statement shows the default value
         */
        showDefaultValue();
        /**
         * ***********CHAPTER TWO*************
         * reference data type
         * reference type just like pointer in C/C++, it cannot be changed or modify
         * once the reference type be confirm, it can refer any familiar
         * like String type
         */
        String str = new String("Hello World!");
        /**
         * constant type, the constant data type in java is distinguish between C/C++
         * in C/C++, we use key word const to represent a constant value, however ,in java
         * we use key word 'final' to represent a constant value;
         */
    }
    public static void showDefaultValue(){
        int varInt = 0;
        byte varByte = 0;
        short varShort = 0;
        long varLong = 0L;
        double varDouble = 0.0D;
        float varFloat = 0.0F;
        /**
         * We suggest add big F behind the value of float instead of small f
         * and it also suggest use double data type instead of float, because
         * they do not have much differences in universal computer
         */
        boolean varBool = false;
        char varChar = '\u0000';
        System.out.println(varInt);
        System.out.println(varByte);
        System.out.println(varShort);
        System.out.println(varLong);
        System.out.println(varDouble);
        System.out.println(varFloat);
        System.out.println(varBool);
        System.out.println(varChar);
    }
}

类型转换

package com.yuque.phil616.datatype;
public class DataTypeConversion {
    /**
     * in fact, data type is not fixed in java, we can converse some of data type
     * into another type of data.
     * byte,short,char—> int —> long—> float —> double
     * byte type take one byte in ram space, however, short take up two
     * and int take up four
     * when we converse small space type into a large space type, it calls
     * auto data converse
     * on the contrary, it calls force data converse.
     * in some of situation, we need add f or F in the value of float
     * and at same reason, we need add d or D in the value of double
     * In the basic of computer, int,short,long,type,char are stored
     * in same way, because they represents the same kind of data
     * which is integer numbers, just with different length.
     * and we can invest more at runoob.com/java/java-basic-datatypes.html
     */
}