ダークホースプログラマー——java-いくつかのよく使われている種類(Object、Scanner、String Buffer、StringBuider)
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———android研修、java研修、java学習型技術ブログ、あなたとの交流を期待しています。――
1 Object類
1 Object類
Object ,
Object
public String toString()---//
public final Class getClass()--- //
public boolean equals(Object obj)-- “ ”。
protected void finalize()----- ,
public int hashCode()----
:
---public String toString()
--getClass().getName() + '@' + Integer.toHexString(hashCode())
(s) , toString() (s.toString() )
。 , , Alt+Shift+s, toString() 。
package importMethod;
class Persion// Persion
{
public String name;
public int age;
public Persion(String name, int age)//
{
this.name = name;
this.age = age;
}
@Override
public String toString()// Object
{
return "Persion [name=" + name + ", age=" + age + "]";
}
}
public class ObjectDemo
{
public static void main(String[] args)
{
Persion persion = new Persion(" ", 25);// Persion
//System.out.println(persion);// Persion ( )
// :importMethod.Persion@56bf1a4a( Persion toString() )
System.out.println(persion);// Persion ( )
// :Persion [name= , age=25]( Persion toString() )
}
}
---public boolean equals(Object obj)
==
-- ,
-- ,
Object equals
, equals , ,
--- instanceof ( , )
2 Scanner類の使い方 :
:--public Scanner(InputStream source)
Scanner in =new Scanner(System.in);
:
System in, :
public static final InputStream in;
:System.in InputStream ( IO )
Scanner :
--public byte nextByte()//
--public int nextInt()// int
--public long nextLong()// long
--public float nextFloat()// float
--public double nextDouble()// double
--public short nextShort()// short
--public String nextLine()// String
package importMethod;
import java.util.Scanner;
public class ScannerDemo
{
private void mian()
{
Scanner in =new Scanner(System.in);//
System.out.println(" ");
int a=in.nextInt();//
System.out.println(" :"+a);//
}
}
---- int String int ,int
,
String
int i=sc.nextInt();String s=sc.nextLine();
;
---A int , Scanner String
package importMethod;
import java.util.Scanner;
public class Scannerproblem
{
public static void main(String[] args)
{
Scanner s=new Scanner(System.in);
int a=s.nextInt();
Scanner i=new Scanner(System.in);// int ,
String string=i.nextLine();// String
System.out.println(a);
System.out.println(string);
}
}
---B , ( String )
package importMethod;
import java.util.Scanner;
public class Scannerproblem
{
public static void main(String[] args)
{
Scanner i =new Scanner(System.in);
String s=i.nextLine();
// String , String
// , ,
System.out.println(s.valueOf(s));
}
}
3 String類 :
A--String()
B--String(byte[] bytes)
C--String(byte[] bytes, int index, int length)
D--String(char[] value)
E--String(char[] value, int indexint count)
F--String(String original)
package com.itheima;
/*
* :
A--String()
B--String(byte[] bytes)
C--String(byte[] bytes, int index, int length)
D--String(char[] value)
E--String(char[] value, int indexint count)
F--String(String original)
*/
public class string_Demo {
public static void main(String[] args) {
// A--String()
String s = new String();
System.out.println("s :" + s.length());
// String(char[] value)
char[] ch = new char[] { 'e', 'd', 'c', 'b', 'a' };
String bs = new String(ch);//
String bs1 = new String(ch, 0, 2);//
System.out.println(bs);
// String(String original)
System.out.println(new String(new String(" !")));//
}
}
: , ( )
( , )
:
String s="hello";
s+="world";
System.out.println(s);// :helloworld
1
String s=new String("hello") String s1="hello" ?
s==s1(false) s.equals(s1)(true)
![ ](https://img-blog.csdn.net/20150428103348930)
2
String s1="hello"
String s2="world"
String s3="helloworld"
s3.equals(s1+s2)//true
s3==s1+s2//false ,
s3=="hello"+"world"//true , , , , ,
String ( )
A--public boolean equals(Object anObject)
,
B--public boolean equalsIgnoreCase(String anotherString)
,
C--public boolean contains(CharSequence s)
D--public boolean endsWith(String suffix)
E--public boolean startsWith(String prefix,int toffset)
F--public boolean isEmpty()
String s=""
s.idEmpty()// true
String s="null"
s.idEmpty()// , , ,
package com.itheima;
/*String :
* A--public boolean equals(Object anObject)
,
B--public boolean equalsIgnoreCase(String anotherString)
,
C--public boolean contains(CharSequence s)
D--public boolean endsWith(String suffix)
E--public boolean startsWith(String prefix,int toffset)
F--public boolean isEmpty()
*/
public class string2 {
public static void main(String[] args) {
String s1 = "Hello";
String s2 = "hello";
System.out.println(s1.equals(s2));// false,
System.out.println(s1.equalsIgnoreCase(s2));// true。
System.out.println(s1.contains("ello"));// true ,
System.out.println(s1.startsWith("He"));// true,
System.out.println(s1.endsWith("lo"));// true,
System.out.println(s1.isEmpty());// false,
}
}
String ( )
A--public int length()//
B--public char charAt(int index)//
C--public int indexOf(int ch)//
D--public int indexOf(int ch,int fromIndex)
// ch
E--public int indexOf(String str,int fromIndex)
// str
F--public int indexOf(String str)//
G--public String substring(int beginIndex)
// ,
H--public String substring(int beginIndex,int endIndex)
// , beginIndex endIndex( , , )
package com.itheima;
/*
* A--public int length()//
B--public char charAt(int index)//
C--public int indexOf(int ch)//
D--public int indexOf(int ch,int fromIndex)
// ch
E--public int indexOf(String str,int fromIndex)
// str
F--public int indexOf(String str)//
G--public String substring(int beginIndex)
// ,
H--public String substring(int beginIndex,int endIndex)
// , beginIndex endIndex( , , )
*/
public class String3 {
public static void main(String[] args) {
String s = "heallo,java";
System.out.println(s.length());//
System.out.println("s , 2 :" + s.charAt(1));// : 2
System.out.println(s.indexOf("jav"));//
System.out.println(s.indexOf("a", 3));// ch
System.out.println(s.substring(2));// :allo,java-- ,
System.out.println(s.substring(0, 3));// :hea---( , ,
}
}
String
A--public int length() B--public char charAt(int index) String
package com.itheima;
public class string4 {
public static void main(String[] args) {
String s="androd,java";
// :
/*
* A--public int length()
* B--public char charAt(int index) String
*/
for (int i = 0; i < s.length(); i++) {
System.out.println(s.charAt(i));
}
}
}
String ( )
byte[] getByteds()
char[] toCharArray()
static String copyValueOf(char[] chs)
static String valueOf(char[] chs)
static String valueOf(int i) ,
String toLowerCase()
String toUpperCase()
String concat(String str)
package importMethod;
public class StringDemo
{
public static void main(String[] args)
{
/*
* String ( )
*
* byte[] getByteds() char[] toCharArray()
*
* static String copyValueOf(char[] chs) static String
* valueOf(char[] chs) static String valueOf(int
* i) ,
*
* String toLowerCase() String toUpperCase() String
* concat(String str)
*/
String s = "java-android";
byte[] bys = s.getBytes();//
System.out.println(" bys :" + bys.length);
char[] ch = s.toCharArray();//
System.out.println(" ch :" + ch.length);
char[] ch1 = new char[]
{ 'a', 'n', 'd', 'r', 'o', 'i', 'd' };
System.out.println(String.valueOf(ch1));//
System.out.println(String.copyValueOf(ch1));//
int a = 100;
System.out.println(String.valueOf(a));// ,
String string = "java AND android";
System.out.println(string.toUpperCase());// ---JAVA AND ANDROID
System.out.println(string.toLowerCase());// ---java and android
String s1 = "hello", s2 = "java";
System.out.println(s1.concat(s2));// -----hellojava
}
}
copyValueOf(char[] chs) valueOf() ?
--copyValueOf(char[] chs) string
-- valueOf() String
String ( )
A--public String replace(char oldChar,char newChar)
oldChar newChar
B--public String replace(String oldChar,String newChar)
String trim() ,
package importMethod;
/*
* A--public String replace(char oldChar,char newChar)
oldChar newChar
B--public String replace(String oldChar,String newChar)
c--public String replace(CharSequence target,CharSequence replacement)
target - char
replacement - char
c---String trim() ,
*/
public class string_tihuan
{
public static void main(String[] args)
{
String olds=" java_an droid ";
String news="hello";
System.out.println(olds.replace(olds, news));// ----hello
System.out.println(olds.replace(news, olds));// --- java_an droid
System.out.println(news.replace("l", "mm"));// ----hemmmmo
System.out.println(olds.trim());// ----java_an droid
}
}
4 StringBuffer/StrigBuider(1) 。
(2)String,StringBuffer/StringBuilder ?
A:String 。 StringBuffer/StringBuilder 。
B:StringBuffer , 。
StringBuilder , 。
(3) :
A:StringBuffer sb = new StringBuffer();// , 16
B:StringBuffer sb = new StringBuffer(50);// ,
C:StringBuffer sb = new StringBuffer("hello");// String.length()+16
(4) :
public int capacity()//
public int length()//
A:
append
StringBuffer , StringBuffer ,
StringBuffer sb=new StringBuffer();
StringBuffer s1=sb.append("hello");
StringBuffer s2=sb.apped("world");
s1==s2//true true, s1 s2
, ,sb.append("hello").append("world");
public StringBuffer insert(int offset,char c)
,
B:
public StringBuffer delete(int start,int end)
start end
public StringBuffer deleteCharAt(int index)
C:
public StringBuffer replace(int start,int end,String str)
[start,end) str
D:
public String substring(int start)
public CharSequence subSequence(int start,int end)
E:
public StringBuffer reverse()//" "----->“ ”
package importMethod;
/*
* public int capacity()//
public int length()//
A:
append
StringBuffer , StringBuffer ,
StringBuffer sb=new StringBuffer();
StringBuffer s1=sb.append("hello");
StringBuffer s2=sb.apped("world");
s1==s2//true true, s1 s2
, ,sb.append("hello").append("world");
public StringBuffer insert(int offset,char c)
,
B:
public StringBuffer delete(int start,int end)
start end ( )
public StringBuffer deleteCharAt(int index)
C:
public StringBuffer replace(int start,int end,String str)
[start,end) str
D:
public String substring(int start)
public CharSequence subSequence(int start,int end)
E:
public StringBuffer reverse()//" "----->“ ”
*/
public class stringBufferDemo
{
public static void main(String[] args)
{
StringBuffer sb = new StringBuffer("android_i am coming!");
System.out.println(" :" + sb.length() + " | 16 : " + sb.capacity());
// : :20 | 16 : 36
StringBuffer sb1 = new StringBuffer();//
sb1.append("android").append(" ").append("hello");
System.out.println(sb1);// :android hello
// ,
System.out.println(sb1.insert(2, 'M'));// :anMdroid hello
//
System.out.println(sb1.deleteCharAt(0));// :nMdroid hello
// ,
System.out.println(sb1.delete(0, 2));// :droid hello-- :( )
//
System.out.println(sb1.replace(0, 2, "MH"));// :MHoid
// hello-- :( )
//
System.out.println(sb1.substring(4));// :d hello
System.out.println(" sb1 :" + sb1 + " :" + sb1.substring(0, 4));// :MHoi
//
System.out.println(" sb1 :" + sb1 + " :" + sb1.reverse());
// : sb1 :MHoid hello :olleh dioHM
}
}
String StringBuffer :
String------->StringBuffer
String s="hello";
: StringBuffer
StringBuffer sb=new StringBuffer(s);
: StringBuffer append()
StringBuffer sb=new StringBuffer();
sd.append(s);//public StringBuffer append(String str)
StringBuffer------->string
StringBuffer sb=new StringBuffer(“hehe”);
:String
String s=new String(sb);
:StringBuffer toString()
String s=sb.toString();////public String toString()
———android研修、java研修、java学習型技術ブログ、あなたとの交流を期待しています。――