Java学习之 String，StringBuilder，StringJoiner

约定不等于承诺〃 2023-06-15 09:47 4阅读 0赞

import java.util.Arrays;
    
    public class javaString { 
    	public static void main (String[] args) { 
    		// String字符串
    		String string = new String("devZhang");
    		System.out.println(string);
    		String name = "Hello World";
    		System.out.println(name);
    		
    		// 长度
    		System.out.println(name.length());
    		// 过滤首尾空白字符（\t \r \n）
    		System.out.println(name.trim());
    		// 过滤首尾空白字符（\t \r \n，及中文空白字符）
    		System.out.println(name.strip());
    		System.out.println(name.stripLeading());
    		System.out.println(name.stripTrailing());
    		// 空字符
    		System.out.println("空字符：" + name.isEmpty());
    		System.out.println("空白字符：" + name.isBlank());
    		
    				
    		// 大小写
    		System.out.println();
    		System.out.println(name);
    		name = name.toUpperCase();
    		System.out.println(name);
    		name = name.toLowerCase();
    		System.out.println(name);
    		
    		// 比较
    		System.out.println();
    		System.out.println(name);
    		System.out.println(name == "hello World");
    		System.out.println(name.equals("hello World"));
    		System.out.println(name.equalsIgnoreCase("hello World"));
    		// 大小比较 =0 A==B, >0 A<B, <0 A>B
    		System.out.println(name);
    		System.out.println(name.compareTo("world")); 
    		System.out.println(name.compareTo("Hello World"));
    		System.out.println(name.compareTo("hello world"));
    		
    		// 子串
    		System.out.println();
    		System.out.println(name);
    		System.out.println("是否包含：" + name.contains("devZhang"));
    		System.out.println("字符串o所在位置：" + name.indexOf("o"));
    		System.out.println("最后一个字符串o所在位置：" + name.lastIndexOf("o"));
    		System.out.println("是否world开头：" + name.startsWith("world"));
    		System.out.println("是否world结尾：" + name.endsWith("world"));
    		System.out.println("提取第2个位置开始的子串：" + name.substring(2));
    		System.out.println("提取第2个位置开始长度为5的子串：" + name.substring(2, 5));
    		
    		// 替换子串
    		System.out.println();
    		System.out.println(name);
    		System.out.println("world 替换成 devZhang：" + name.replace("world", "devZhang"));
    		
    		// 分割字符串
    		System.out.println();
    		System.out.println(name);
    		String names[] = name.split(" ");
    		System.out.println("分割字符串为数组：" + Arrays.toString(names));
    		
    		// 拼接字符串
    		System.out.println();
    		System.out.println(name);
    		System.out.println("拼接数组为字符串：" + String.join(",", names));
    		
    		// 类型转换
    		System.out.println();
    		String numStr = "098880";
    		System.out.println(numStr);
    		String intStr = String.valueOf("123500");
    		System.out.println(intStr);
    		Boolean boolValue = Boolean.parseBoolean("true");
    		System.out.println(boolValue);
    		int intValue = Integer.parseInt("123456");
    		System.out.println(intValue);
    		
    		// char互转
    		System.out.println();
    		char[] charValue = name.toCharArray();
    		System.out.println(charValue);
    		String strValue = new String(charValue);
    		System.out.println(strValue);
    		
    		// 编码 byte数组
    		byte[] byteValue1 = name.getBytes();
    		System.out.println(Arrays.toString(byteValue1));
    		
    
    		// 字符串连接
    		System.out.println(name.concat(", haha~"));
    		System.out.println(name + ", ao~~~");
    		// 格式化字符串
    		String strFormat = String.format("%s is from %s", name, "深圳");
    		System.out.println(strFormat);
    		System.out.printf("%s is learning Java", name);
    		
    		
    		/* * StringBuilder，它是一个可变对象，可以预分配缓冲区，这样，往StringBuilder中新增字符时，不会创建新的临时对象. * * */
    		StringBuilder strBuilder = new StringBuilder();
    		for (int i = 0; i < 30; i++) { 
    			// append 字符拼接
    			strBuilder.append(i);
    			strBuilder.append(","); 
    		}
    		System.out.println(strBuilder);
    		// 字符删除
    		strBuilder.delete(strBuilder.length() - 1, strBuilder.length());
    		System.out.println(strBuilder);
    		strBuilder.deleteCharAt(10);
    		System.out.println(strBuilder);
    		// 字符替换
    		strBuilder.replace(10, 11, "devZhang,");
    		System.out.println(strBuilder);
    		
    		// 链式操作
    		StringBuilder nameBuilder = new StringBuilder();
    		nameBuilder.append("devZhang").append(" is learning").append("Java.");
    		System.out.println(nameBuilder);
    		
    		/* * StringJoiner用分隔符拼接数组 */
    		String[] names = { "devZhang", "devWang", "devLi"};
    		System.out.println(Arrays.toString(names));
    		StringJoiner nameJoiner = new StringJoiner(",");
    		for (String name : names) { 
    			nameJoiner.add(name);
    		}
    		System.out.println(nameJoiner);
    
    
    		
    	}
    }