The Java Language

CS 161 - Java

String and System objects

String - not a primitive, an Object

• A special Object with some built-in language support.

• Over 20 methods (many more if you count overloading), e.g.,
  • equals(String);
  • equalsIgnoreCase(String);
  • indexOf(int);
  • indexOf(String);
  • lastIndexOf(String);
  • substring(int);

• Quoted strings are made into String objects automatically:

  "This is a String"
  

• Strings overload the + operator to mean "concatenate" (and create a new String)

• String objects are immutable once created they never change; you can only create a new string

  Tip: If you need to change a String's contents a lot, use a StringBuffer object.

    public String toString() {
      StringBuffer result = new StringBuffer();
      result.append( "Name:" );
      result.append( name );
      result.append( "\nGMU Id:" );
      result.append( GMUid );
      result.append( "\nemail:" );
      result.append( email );
      result.append( "\ndate:" );
      result.append( now );
      return result.toString();
    }
  

  is better than

    public String toString() {
      String result;
      result = "Name:" + name +
               "\nGMU Id:" + GMUid +
               "\nemail:" + email +
               "\ndate:" + now;
      return result;
    }
  

  The latter creates 8 String objects as a result of all the + operators.

System

• in - the "standard" input stream

• out - the "standard" output stream

• err - the "standard" error output stream

• Over 18 methods itself, over 32 counting those of in, out, and err

String and System are part of the Java API's java.lang package

jwd