Character类

package com.yuque.phil616.builtin;
public class CharacterClass {
    char ch = 'a';
    // the form of character in Unicode:
    // 这个字符是栈内存储存的
    char uniChar = '\u039A';
    // array of a character:
    char[] charArray ={ 'a', 'b', 'c', 'd', 'e' };
    void testCharacterClass(){
        Character ch = 'a';
        /*
         * 下面的语句是标准的通过对象来创建一个字符类
         *  Character ch = new Character('a');
         */
        // code above is the usage of Character object
        // the original character of 'a' boxing to Character object chs
        Character chs = 'a';
    }
}

Math类

package com.yuque.phil616.builtin;
public class MathClass {
        /**
         * Java提供了八种基本的数据类型
         * 不过在开发过程中如果需要使用对象的时候，将基础的类进行封装boxing
         * 为了解决类的问题，java提供了如下类进行打包和拆包
         * the relations between them look like this.
         * Object ->|---Character
         *          |---Boolean
         *          |---Number --->|---Byte
         *                         |---Short
         *                         |---Integer
         *                         |---Long
         *                         |---Float
         *                         |---Double
         */
        Integer oi = 1;
        /**
         * for easy to develop and calculate,Java provide Math class.
         * the methods inside this class can help us to calculate special
         * math problems.
         *
         */
        void mathFunc() {
            System.out.println("Sin of 90 degree " + Math.sin(Math.PI / 2));
            System.out.println("cosine of 0 degree " + Math.cos(0));
            System.out.println("tangent of 60 degree " + Math.tan(Math.PI / 3));
            System.out.println("the arc-tangent of 1 " + Math.atan(1));
            System.out.println("degrees of π/2 " + Math.toDegrees(Math.PI / 2));
            System.out.println(Math.PI);
        }
}

String类

package com.yuque.phil616.builtin;
public class StringClass {
    /**
     * String class is a very usual class in java.
     * Before the examples, we need to know some computer
     * concepts.
     * Public areas and Heap
     * Public areas are the common ram space, it stored the
     * local variables and some strings.
     * Heap is a spacial area in ram.
     * Heap can stored objects with new operator.
     */
    String str1 = "phil616";
    String str2 = new String("phil616");
    /**
     * str1 and str2  have the same context,however the java won't
     * think that.
     */
    void testStrings(){
        if(str1 == str2) {
            System.out.print("they are same");
        }else{
            System.out.print("they are not same");
        }
    }
    /**
     * key word 'new' comes from C++, it will create a empty space in
     * heap to stored information. In this case, different object are
     * not the same thing though they have the same context.
     */
    String str3 = new String("phil616");
    //objects belongs different heap ares, so they are not same concept
    //of values
    /**
     * different from the String, the objects created by StringBuffer
     * or StringBuilder are allow to change and operate by its methods
     * The methods below will show the usage of this classes
     */
    void StringBuilderTest(){
        StringBuilder sb = new StringBuilder(10);
        sb.append("phil616..");
        System.out.println(sb);
        sb.append("!");
        System.out.println(sb);
        sb.insert(8, "Java");
        System.out.println(sb);
        sb.delete(5,8);
        System.out.println(sb);
    }
    //When we are force to keep the thread secure, we have to use StringBuffer
    void StringBufferTest(){
        StringBuffer sBuffer = new StringBuffer("github public website");
        sBuffer.append("www");
        sBuffer.append(".github");
        sBuffer.append(".com");
        System.out.println(sBuffer);
    }
}