String string type uses detailed Getting Started 25

String string type uses detailed entry.

• String class represents string type, all text strings (e.g. "abc") Java programs are implemented as instances of this class. In other words, Java programs in all double-quoted strings, is an object of the String class.
• String Class In java.lang package, so when used need not guide the package.

Features of the String class

String String class definition also called immutable string.

1. Immutable strings, their value can not be changed after creation, we find that the string change actually points to a new string object (before the string will be automatically recovered)
2. It is because the value of the string object is immutable, they can be shared
3. Corresponds to the array of characters (char []) on the effect of the string, but the underlying principle is the array of bytes (byte [])

Other ways to create a string object description

• public String () to create a blank string object does not contain any content

• public String (char [] chs) based on the contents of an array of characters, to create a string object

    可以吧字符数组的类容转变成字符串
    char[] chs = {'a','b','我','中','国'};
    String rs = new String(chs);
    System.out.println(rs);//ab我中国
  

• public String (byte [] bys) according to the content byte array to create a string object

    		byte[] bytes = {97 , 98 , 99 , 65 , 66 , 67};
            String rs1 = new String(bytes);
            System.out.println(rs1);//abcABC
  

• String s = "abc"; create a direct assignments of the String object, content is the classic abc written.!

note:

• Direct definition of "string content" on the string constant pool.

• out of the new objects in the heap memory string.

    34 String name1 = "赵丽颖"; // 这里有创建对象的，对象放在常量池！
    35 String name2 = "赵丽颖"; // 这里没有创建对象，共享了34行的字符串常量。
    所以这里只创建了一个字符串对象
  
  
    String name3 = new String("赵丽颖"); // 这里创建的字符串对象会放到堆内存中一份！常量池中也有一份！
    String name4 = "赵丽颖" ;  // 对象在常量池中！所以没有重新创建对象！
    所以这里也只创建了一个字符串对象
  

public class StringDemo {
    public static void main(String[] args) {
        // 1.String类型定义一个字符串对象变量:name
        String name = "cx";
        name += "学生" ; // name = name + "老师"
        System.out.println(name); // cx学生

        String name1 = "赵丽颖"; // 这里有创建对象的，对象放在常量池！
        String name2 = "赵丽颖"; // 这里没有，共享了34行的字符串常量。
        System.out.println(name1 == name2); // name1和name2指向的是同一个地址！！

        // 1.创建字符串对象的其他方式:调用有参数构造器。
        String name3 = new String("赵丽颖"); // 这里创建的字符串对象会放到堆内存中一份！！
        String name4 = "赵丽颖" ;  // 对象在常量池中！建议这样定义！
        System.out.println(name3);
        System.out.println(name4);

        // 2.  public String(char[] chs) 根据字符数组的内容，来创建字符串对象(了解)
        char[] chs = {'a','b','我','中','国'};
        String rs = new String(chs);
        System.out.println(rs);

        // 3.public String(byte[] bys) 根据字节数组的内容，来创建字符串对象
        byte[] bytes = {97 , 98 , 99 , 65 , 66 , 67};
        String rs1 = new String(bytes);
        System.out.println(rs1);
    }
}