Java String String commonly used method in detail and use

String String commonly used methods:

length()、equals()、startWith()、endsWith()、compareTo()、contains()、indexOf()、lastIndexOf()、substring()、trim()；

A, public int length () is used:

By this method:

Gets a String object character sequence length (number of characters);

The following code ↗:

// public int length() 计算字符串的长度，字符个数
	    String word = "我在学习JavaSE";
	    System.out.println(word.length());
	    System.out.println("JavaSE的长度："+"JavaSE".length());

Character sequence length: 1 counting from the beginning, is not 0;

Code output:

Length of JavaSE: 6

Two, public boolean equals (String s) used:

By this method:

Comparative String object if the current character sequence with the character sequence s is equal, regardless of their reference values, the output is equal to true, the output is not equal to false;

The following code ↗:

            String wordz = "ITM" + "ITM" ;
	    String wordx = words + worda ;
	    //equals只判断两个字符序列的常量是否相等，不考虑对象引用是否相等
	    if(wordz.equals(wordx)){
	    	System.out.println("hj == jh");
	    }else{
	    	System.out.println("hj != jh");
	    }
	    
	    // “ == ” 要判断两个字符序列的常量是否相等，也要判断对象引用是否相等，都相等才为true
	    if(wordz == wordx){
	    	System.out.println("hj == jh");
	    }else{
	    	System.out.println("hj != jh");
	    }

Meaning the code, == and equals (), it is not the same;

Code output:

== JH Hj
Hj! = JH

Three, public boolean startWith (String s) used:

By this method:

Comparing the current sequence of characters String object prefix is equal to the character sequence s, is equal to the output true, unequal output false;

The following code ↗:

            String tom = "今天是个好天气";
	    System.out.println("判断前缀，startsWith："+tom.startsWith("今天"));

Code output:

true

Four, public boolean endsWith (String s) of use:

By this method:

Comparing the current sequence of characters String object suffix is equal to the character sequence s, is equal to the output true, unequal output false;

The following code ↗:

            String toms = "明天要出太阳了";
	    System.out.println("判断后缀，endsWith："+toms.endsWith("太了"));

Code output:

false

Five, public int compareTo (String s) of use:

By this method:

Comparing two sequences string, case sensitive, with reference to the Unicode standard character size comparison table;

1, when the same character sequence s String object, the method returns 0;

2, when the character sequence is larger than s String object, the method returns a value;

3, when the character sequence smaller than s String object, the method returns a negative value;

The following code ↗:

//当 String 对象的字符序列与 s 的 相同，则方法返回 0 ；
            String hellos = "abcd";
	    String hellox = "abcd";
	    String helloz = "ABCD";
	    System.out.println(hellos.compareTo(hellox));
	    System.out.println(hellos.compareTo(helloz));

//当 String 对象的字符序列比 s 的 大 ，则方法返回一个 正值 ；
            String hellos = "abcd";
	    String hellox = "abc";
	    System.out.println(hellos.compareTo(hellox));

//当 String 对象的字符序列比 s 的 小 ，则方法返回一个 负值 ；
            String hellos = "abc";
	    String hellox = "abcd";
	    System.out.println(hellos.compareTo(hellox));

Code output:

0
32
1
-1

Six, public boolean compareToIgnoreCase (String s) of use:

This method compareTo (String s) is the same, the only difference is that the method is not case-sensitive;

The following code ↗:

//当 String 对象的字符序列与 s 的 相同，则方法返回 0 ，不区分大小写 ；
	    String hellos = "abcd";
	    String helloz = "ABCD";
	    System.out.println(hellos.compareToIgnoreCase(helloz));

Code output:

Seven, public boolean contains (String s) of use:

By this method:

String object determines whether the current character sequence contains a sequence of characters parameter s, includes an output true, does not include an output false;

The following code ↗:

            String Fa = "Hello you world";
	    System.out.println(Fa.contains("Hl"));
	    System.out.println(Fa.contains(" wo"));

Code output:

false
true

Eight, public int indexOf (String s), public int indexOf (String s, int startpoint) use:

1, a sequence of characters from the index position 0 String object to start retrieving the first occurrence of the character sequence parameter s, and returns the location;

2, when the corresponding character is not retrieved, the return value is -1;

3, the space character can be considered;

public int indexOf (String s) Method:

Code is as follows ↗:

//用于判断字符最先出现的位置
            String cases = "hello are you,thank you";
	    System.out.println(cases.indexOf("ar"));     
	    System.out.println(cases.indexOf("ae"));

Code output:

6
-1

public int indexOf( String s , int startpoint ) 方法：

Code is as follows ↗:

            String cases = "hello are you,thank you";
	    System.out.println(cases.indexOf("llo",1));   //用于判断指定位置的字符
	    System.out.println(cases.indexOf("llo",11));   //用于判断指定位置的字符

Code output:

2
-1

Nine, public int lastIndexOf (String s) of use:

1, a sequence of characters from the index position 0 String object to begin retrieving character sequence parameter s last seen position, and returns the location;

The following code ↗:

            String cases = "hello are you,thank you";
	    System.out.println(cases.lastIndexOf("o"));  //用于判断字符最后出现的位置
	    System.out.println(cases.lastIndexOf("a"));  //用于判断字符最后出现的位置
	    
	    String casex = "https://fanyi.baidu.com//?aldtype=85&keyfrom";
	    System.out.println(casex.indexOf("//"));      //用于判断字符最先出现的位置
	    System.out.println(casex.lastIndexOf("//"));    //用于判断字符最后出现的位置

Code output:

21
16
6
23

Ten, public boolean substring (int startpoint) use:

By this method:

Counted from 0, startpoint position of a character sequence replication String object to a character in the last position to give a new String object;

The following code ↗:

            String sub = "梦想着，怀念着，希望着" ;
	    String su = sub.substring(1);
	    System.out.println(su);

Code output:

Thinking, miss, hoping the

Eleven, public boolean substring (int start, int end) is used:

By this method:

Counted from 0, the sequence of characters in a String object copy start position to the end-1 character at a position to give a new String object;

The following code ↗:

            String sub = "梦想着，怀念着，希望着" ;
	    String ss = sub.substring(1, 5);   //5-1
	    System.out.println(ss); 
	    String sx = sub.substring(4, 6);   //6-1
	    System.out.println(sx);

Code output:

Thinking, pregnant
miss

Twelve, public boolean trim () is used:

trim () method is also obtained a new String object, but the character sequence new String object of the current sequence of characters String object before and after removing space characters in sequence;

The following code ↗:

            String wordd = " and you,go to eat fish " ;
	    System.out.println(wordd+",Yes");
	    String wordds = wordd.trim();
	    System.out.println(wordds+",Yes");

Code output:

and you,go to eat fish ,Yes
and you,go to eat fish,Yes

LagerSwan,

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Private letter concerns

Java String String commonly used method in detail and use

String String commonly used methods:

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