javaSE-Day3-String类中常用方法

一、字符串与字符

1.public String(char[] value)	//（构造）字符数组》》字符串

	public class TestString {
		public static void main(String args[]) {
			char data[] = new char[] {'a', 'b', 'c'};
			String arr = new String(data);
			System.out.println(arr); 		
		}
	

2.public String(char[] value, int offset, int count)	//（构造）指定范围

3.public char charAt(int index)	//（普通）取得字符串指定位置字符

	public class TestString {
		public static void main(String args[]) {
			String arr = "Hello";
			char c = arr.charAt(1);
			System.out.println(c); 		
		}
	}

4.public char[] toCharArray()	//(普通) 字符串》》字符数组

	public class TestString {
		public static void main(String args[]) {
			String arr = "Hello";
			char data[] = arr.toCharArray();
			int l = data.length;
			for(int i = 0; i < l; i++) {
				System.out.print(data[i] + "、"); //字符数组
			}
			System.out.println();
			System.out.println(arr); //字符串
		}
	}

二、字符串与字节

1.public String(byte[] bytes)	//（构造）字节数组》》字符串

2.public String(byte[] bytes, int offset, intlength)	//（构造）指定范围

3.public byte[] getBytes()	//（普通）字符串》》字节数组

public class TestString {
	public static void main(String args[]) {
		String msg = "Hello";
		byte data[] = msg.getBytes();
		System.out.println(new String(data));
	}
}

4.public byte[] getBytes(String charsetName)	//(普通) 编码转换

	throws UnsupportedEncodingException	

三、子符串比较

1.public boolean equals(String anObject)	//（普通）判断两个字符串是否相等，区分大小写

2.public boolean equalsIgnoreCase(String anotherString)	//（普通）不区分大小写

3.public int compareTo(String anotherString)	//（普通）比较两个字符串大小（按照字符编码）

	public class TestString {
		public static void main(String args[]) {
			String arr = "Hello";
			String brr = "Hello";
			String crr = "hELLO";
			//区分大小写
			System.out.println(arr.equals(brr));
			System.out.println(arr.equals(crr));
			//不区分大小写
			System.out.println(arr.equalsIgnoreCase(brr));
			System.out.println(arr.equalsIgnoreCase(crr));
			//字符串大小关系（按照字符编码）
			System.out.println(arr.compareTo(brr));
			System.out.println(arr.compareTo(crr));
		}
	}

四、字符串查找

1.public boolean contains(String s)	//（普通）判断字符串是否存在

public class TestString {
	public static void main(String args[]) {
		String arr = "Hello";
		System.out.println(arr.contains("Hello"));
		System.out.println(arr.contains("World"));
	}
}

2.public int indexOf(String str)	//（普通）从头查找字符串位置，找不到返回-1

3.public int indexOf(String str, int fromIndex)	//(普通)指定位置

4.public int lastIndexOf(String str)	//(普通)从后往前

5.public int lastIndexOf(String str, int fromIndex)	//

6.public boolean startsWith(String prefix)	//（普通）判断是否以指定的字符串开头

7.public boolean starsWith(String prefix, int toffset)	//

8.public boolean endWith(String suffix)	//

	public class TestString {
		public static void main(String args[]) {
			String msg = "Hello";
			System.out.println(msg.indexOf("l"));
			System.out.println(msg.indexOf("l", 3));
			System.out.println(msg.lastIndexOf("l", 3));
			System.out.println(msg.startsWith("H"));
			System.out.println(msg.endsWith("H"));
		}
	}

五、字符串替换

1.public String replaceAll(String regex, String replacement)	//（普通）全替换

2.public String replaceFrist(String regex, String repalcement)	//

	public class TestString {
		public static void main(String args[]) {
			String msg = "Hello";
			System.out.println(msg.replaceAll("l", "A"));
			System.out.println(msg.replaceFirst("l", "A"));
		}
	}

六、字符串拆分 

1,public String[] split(String regex)	//(普通)全拆分

2.public String[] split(String regex, int limit)	//

	public class TestString {
		public static void main(String args[]) {
			String msg = "Hello";
			String data[] = msg.split(" "); //空格
			for(int i = 0; i < data.length; i++) {
				System.out.println(data[x]);
			}
		}
	}

七、字符串截取

public String substring(int beginIndex)	//由开始截取

public String substring(int beginIndex, int endIndex)	//

	public class TestString {
		public static void main(String args[]) {
			String msg = "Hello";
			System.out.println(msg.substring(2));
			System.out.println(msg.substring(2, 3));		
		}
	}

八、其他方法

1.public boolean isEmpty()	//是否为空（""）,不是Null

2.public int length()	//取得字符串长度

3.public String toLowerCase()	//转小写

4.public String toUpperCase()	//转大写

5.public String trim()	//去掉左右空格