String

1. String的内存分配情况

public class String1 
{
	public static void main(String[] args)
	{
		String s1 = "hello";
		String s2 = "hello";
		String s3 = new String("hello");
		String s4 = new String("hello");
		System.out.println("s1==s2: "+(s1==s2));		//== 比较的内存地址  //true
		System.out.println("s2==s3: "+(s2==s3));		//false
		System.out.println("s3==s4: "+(s3==s4));		//false	
		System.out.println("s1 equals s2: "+s1.equals(s2));	//true
		System.out.println("s2 equals s3: "+s2.equals(s3));	//true
		System.out.println("s3 equals s4: "+s3.equals(s4)); //true  //equals 默认比较两对象的地址
		s2 = "world";
		System.out.println(s1);							//hello
	}
}

运行结果：


s1==s2: true
s2==s3: false
s3==s4: false
s1 equals s2: true
s2 equals s3: true
s3 equals s4: true
hello


2.String的构造方法

//使用字节数组或者整形数组都可以构造一个字符串
public class String2 {


	public static void main(String[] args) 
	{
		byte[] a = {97,98,99,100,101};
		String s = new String(a);
		System.out.println(s); 	//使用一个字节数组构建一个字符串
		
//		public String(byte[] bytes,int offset, int length)
//		bytes - 要解码为字符的 byte
//		offset - 要解码的第一个 byte 的索引
//		length - 要解码的 byte 数 
		
		s = new String(a,1,3);	//0是第一个
		System.out.println(s);
		
		char[] c = {'c','h','a','r'};
		s = new String(c);
		System.out.println(s);
		s = new String(c,2,2);
		System.out.println(s);
		
		int[] i = {97,98,99};
		s = new String(i,0,3);	//没有s = new String(i);的方法
		System.out.println(s);
		
		s = new String("abc");
		System.out.println(s);
	}
}

运行结果：


abcde
bcd
char
ar
abc
abc
 


3.String方法


① 获取方法

//int length()  获取字符串的长度
//char charAt(int index) 获取特定位置的字符 (角标越界)
//int indexOf(String str) 获取特定字符的位置(overload)
//int lastIndexOf(int ch) 返回指定字符在此字符串中最后一次出现处的索引。


public class String3
{
	public static void main(String[] args) 
	{
		String s = "abcdecdcd";
		System.out.println(s.length());		//9
		char c = s.charAt(2);
		System.out.println(c);				//c
		int w = s.indexOf('b');
		System.out.println(w);				//1
		w = s.lastIndexOf('c');
		System.out.println(w);				//7
		
	}
}
 

②判断方法




//boolean endsWith(String str) 是否以指定字符结束
//boolean isEmpty()是否长度为0 如：“” null V1.6
//boolean contains(CharSequences) 是否包含指定序列 应用：搜索
//boolean equals(Object anObject) 是否相等
//boolean equalsIgnoreCase(String anotherString) 忽略大小写是否相等




public class String4 
{
public static void main(String[] args) 
{
String s = "abcdefg";
System.out.println(s.endsWith("fg")); //true
System.out.println(s.isEmpty()); //false
System.out.println(s.contains("gh")); //false
String s1 = "ABCDEFG";
System.out.println(s.equalsIgnoreCase(s1));//ture

}
}
③转换方法


String(char[] value) 将字符数组转换为字符串


String(char[] value, int offset, int count)


Static String valueOf(char[] data)


static String valueOf(char[] data, int offset, int count)


char[] toCharArray()  将字符串转换为字符数组


④ 其他

import java.util.Arrays;




//String replace(char oldChar, char newChar) 替换
//String[] split(String regex) 切割
//String substring(int beginIndex) 
//String substring(int beginIndex, int endIndex)截取字串
//String toUpperCase() 转大写
//String toLowerCase() 转小写
//String trim() 去除首尾空格
public class String5
{
	public static void main(String[] args) 
	{
		String s1 = "  aabbccd";
		String s2 = s1.replace('b', 'c');
		System.out.println(s2);				//  aaccccd
		s2 = s1.replace("bb", "ccccccc");
		System.out.println(s2);				//  aacccccccccd
		s2 = s1.substring(2);
		System.out.println(s2);				//bbccd
		s2 = s1.substring(2,4);
		System.out.println(s2);				//bb
		String[] a = s1.split("c");
		System.out.println(Arrays.toString(a));	//[  aabb, , d]
		s2 = s1.trim();
		System.out.println(s2);				//aabbccd去除首尾的空格
		s2 = s1.toUpperCase();
		System.out.println(s2);				//  AABBCCD
	}
}