java中String的基本用法

class toStringText
{
 private int a = 10;
 private float b = 10.0f;
 private double d = 100.0d;
 
 public static void main(String[] args)
 {
  int a = 10;
  float b = 10.0f;
  double d = 100.000000d;
  char[] ch = {'h','e','l','l','o'};
  System.out.println(String.valueOf(a));
  System.out.println(String.valueOf(b));
  System.out.println(String.valueOf(d));
  System.out.println(String.valueOf(ch,2,3));
  
  boolean bool = false;
  System.out.println(String.valueOf(bool));
  System.out.println(bool);
  String str = "    hello world!   ";
  System.out.println(str.trim()); //忽略字符串中的前部空格和後部空格  
  
  System.out.println(str.toUpperCase());//轉化爲大寫
  System.out.println(str.toLowerCase());//小寫
  char[] ch2 = str.toCharArray(); //字符串轉化爲字符數組
  System.out.println(str.trim().startsWith("hello"));
 }
}