Q:

How to type String content:encoded = "Hello"; in java?

How to type String content:encoded = "Hello";  in java ? 
Eclipse keep telling me syntax error on tokens delete these tokens ?
setDescription(String content:encoded) {
    _description = content:encoded;
}

A:

Because content:encoded is a syntax error. Name in java only accept letters numbers $ and "_". The rule might allow some other characters but it should be pretty much it. Also a variable cannot start with a number. 
To be clear, remove the : from the variable name because : is illegal in a name and might have an other meaning in the language. 
Quote from the article below:

Variable names are case-sensitive. A variable's name can be any legal identifier — an unlimited-length sequence of Unicode letters and
  digits, beginning with a letter, the dollar sign $, or the
  underscore character _. The convention, however, is to always begin
  your variable names with a letter, not $ or _. Additionally, the
  dollar sign character, by convention, is never used at all. You may
  find some situations where auto-generated names will contain the
  dollar sign, but your variable names should always avoid using it. A
  similar convention exists for the underscore character; while it's
  technically legal to begin your variable's name with _, this
  practice is discouraged. White space is not permitted.
Subsequent characters may be letters, digits, dollar signs, or underscore characters.

Here read more about it: http://docs.oracle.com/javase/tutorial/java/nutsandbolts/variables.html

A:

if you are creating method setDescription then it whould be:
public void setDescription(String content_encoded) {
    _description = content_encoded;
}

Here 

public is modifier
void is return type
setDescription is method name
String is parameter type
content_encoded is Variable that is holding string value.

