//String類
public class Main
{
	public static void main(String[] args)
	{
		String str1=new String();
		String str2=new String("abcd");
		char[] charArray=new char[] {'D','E','F'};
		String str3=new String(charArray);
		System.out.println(str2);
		System.out.println(charArray);
		System.out.println(str3);
	}
}
 

public class Main
{
	public static void main(String[] args)
	{
		String str="abcd";
		char[] charArray=str.toCharArray();//把字串轉化為字元陣列
		for(int i=0;i<str.length();i++)
		{
			System.out.print(charArray[i]);
		}
		System.out.println();
		System.out.println(String.valueOf(12));//把一個整形化為支付串
		System.out.println(str.toUpperCase());//把字串變成大寫
		String str1="abck";
		System.out.println(str1.replace("a","A"));
		System.out.println(str1.equals(str));
	}
}
 

//Math類
public class Main
{
	public static void main(String[] args)
	{
		System.out.println(Math.abs(-1));//絕對值
		System.out.println(Math.ceil(5.1));//去小數
		System.out.println(Math.floor(5.9));//有小數進一
		System.out.println(Math.round(4.6));//四捨五入
		System.out.println(Math.random());//隨機取值
	}
}