java String操作

package shaohv.String;

import java.util.Formatter;

public class StringInit {
	//for 1.
	public static String upcase(String s){
		return s.toUpperCase();
	}
	
	//for 2.
	public static void change(String s){
		s = "changing";
		System.out.println("in change String is: "+s);
	}
	
	//for 4.
	class Receipt{
		private double total = 0;
		private Formatter f = new Formatter(System.out);
		public void printTitle(){
			f.format("%-15s %5s %10s\n", "Term","Qty","Price");
			f.format("%-15s %5s %10s\n", "----","---","-----");
		}
		public void myprint(String name, int qty, double price){
			f.format("%-15.15s %5d %10.2f", name,qty,price);
		}
	}
	
	public static void main(String[] args){
		/*
		 * 1. 测试一下声明与初始化的关系
		 * 结果说明：String可以先声明，然后再初始化
		 */
		System.out.println("\n1、***********************************");
		String a = "hello";
		String b = null;
		System.out.println("String a is: "+a);
		System.out.println("String b is: "+b);
		a = "world";
		b = "what";
		System.out.println("String a is: "+a);
		System.out.println("String b is: "+b);
		
		/*
		 * 2. 测试一下String的不可变性
		 * 结果说明： String类型是不可变的，自己体会一下。
		 */
		System.out.println("\n2、***********************************");
		String c = "okay";
		String d = "good";
		System.out.println("before upcase c is: "+c);
		String cc = upcase(c);
		System.out.println("cc is: "+cc);
		System.out.println("after upcase c is: "+c);
		
		System.out.println("before change d is: "+d);
		change(d);
		System.out.println("after upcase d is: "+d);
		
		/*
		 * 3. 格式化输出System.out.format
		 */
		System.out.println("\n3、***********************************");
		int e = 20974 ;
		float f = 34345.7234f;
		double g = 3.1215926d;
		System.out.format("row 1: [%d,%f,%f]\n", e,f,g);
		System.out.printf("row 2: [%d,%f,%f]\n", e,f,g);
		
		/*
		 * 4. Formatter类 
		 */
		System.out.println("\n4、***********************************");
		StringInit stringInit = new StringInit();
		Receipt receipt = stringInit.new Receipt();
		receipt.printTitle();
		receipt.myprint("jack is my friend", 4, 3.1415926);
		
		/*
		 * 5. String.format接受与Formatter.format同样的参数
		 * 输出一个String对象
		 */
		System.out.println("\n5、***********************************");
		String h = String.format("(t%d,q%d) %s",3,7,"write failed!" );
		System.out.println(h);
	}
}

结果输出：

1、***********************************
String a is: hello
String b is: null
String a is: world
String b is: what

2、***********************************
before upcase c is: okay
cc is: OKAY
after upcase c is: okay
before change d is: good
in change String is: changing
after upcase d is: good

3、***********************************
row 1: [20974,34345.722656,3.121593]
row 2: [20974,34345.722656,3.121593]

4、***********************************
Term              Qty      Price
----              ---      -----
jack is my frie     4       3.14
5、***********************************
(t3,q7) write failed!