Javaの開発経験 - ストリングクラスを使用します

Javaの開発経験 - ストリングクラスを使用します

文字列s = NULL;ヒープメモリ割り当てられていない//ヌル空間   
//任意のオブジェクト格納されずに、メモリ空間を割り当て、文字列を   
列A =「」; //メモリ空間を割り当て、文字列オブジェクトが保存され

一般的な方法

public class StringTest {
public static void main(String[] args) {
	String str1 = new String();
	System.out.println(str1);
	String str2 = new String("asdf");
	System.out.println(str2);
	char[] value = {'a','b','c','d'};
	String str3 = new String(value);
	System.out.println(str3);
	String str4 = new String(value, 1, 2);
	System.out.println(str4);
	byte[] strb = new byte[]{65,66};
	String str5 = new String(strb);
	System.out.println(str5);
	String str = new String("asdfzxc");
	int strlength = str.length();
	System.out.println(strlength);
	char ch = str.charAt(4);//ch = z
	System.out.println(ch);
	//该方法从beginIndex位置起，从当前字符串中取出剩余的字符作为一个新的字符串返回
	String str6 = str.substring(2);//str2 = "dfzxc"
	System.out.println(str6);
	//该方法从beginIndex位置起，从当前字符串中取出到endIndex-1位置的字符作为一个新的字符串返回。
	String str7 = str.substring(2,5);//str3 = "dfz"
	System.out.println(str7);
	
	String str8 = new String("abc");
	String str9 = new String("ABC");
	int a = str8.compareTo(str9);//a>0
	int b = str8.compareToIgnoreCase(str9);//b=0
	boolean c = str8.equals(str9);//c=false
	boolean d = str8.equalsIgnoreCase(str9);//d=true
	
	//相当于String str = "aa"+"bb"+"cc";
	String str10 = "aa".concat("bb").concat("cc");
	System.out.println(str10);
	
	String str11 = "I am a good student";
	//于查找当前字符串中字符或子串，返回字符或子串在当前字符串中从左边起首次出现的位置，若没有出现则返回-1。
	int aa = str11.indexOf('a');//a = 2
	int bb = str11.indexOf("good");//b = 7
	//从fromIndex位置向后查找。
	int cc = str11.indexOf("w",2);//c = -1
	//区别在于该方法从字符串的末尾位置向前查找。
	int dd = str11.lastIndexOf("a");//d = 5
	int ee = str11.lastIndexOf("a",3);//e = 2
	
	String str00 = new String("asDF");
	String str111 = str00.toLowerCase();//str1 = "asdf"
	System.out.println(str111);
	String str222 = str00.toUpperCase();//str2 = "ASDF"
	System.out.println(str222);
	
	String str0 = "asdzxcasd";
	String str100 = str0.replace('a','g');//str1 = "gsdzxcgsd"
	String str200 = str0.replace("asd","fgh");//str2 = "fghzxcfgh"
	String str300 = str0.replaceFirst("asd","fgh");//str3 = "fghzxcasd"
	String str400 = str0.replaceAll("asd","fgh");//str4 = "fghzxcfgh"
	
	String str33 = " a sd ";
	String str13 = str33.trim();
	System.out.println(str13);
	
	String strR = "asdfgh";
	boolean aA = strR.startsWith("as");//a = true
	System.out.println(aA);
	boolean bB = strR.endsWith("gh");//b = true
	System.out.println(bB);
	
	String strC = "student";
	System.out.println(strC.contains("stu"));//true
	System.out.println(strC.contains("ok"));//false
	
	String strS = "asd!qwe|zxc#";
	String[] strss = str.split("!|#");
	//str1[0] = "asd";str1[1] = "qwe";str1[2] = "zxc";
	System.out.println(strss.toString()); 
	
	//字符串转换为基本类型
	int n = Integer.parseInt("12");
	System.out.println(n);
	float f = Float.parseFloat("12.34");
	System.out.println(f);
	double D = Double.parseDouble("1.124");
	System.out.println(D);
	
	//基本类型转换为字符串类型
	String s111 = String.valueOf(12);
	System.out.println(s111);
	String s122 = String.valueOf(12.34);
	System.out.println(s122);
	
	//进制转换
	String binaryString = Long.toBinaryString(7);
	System.out.println(binaryString);
}
}