String str = "I am a Chinese people." ;
String newStr="";
String strArr[] = str.spit(" ");
for(int i=0;i<strArr.length;i++){
  if(str.equals("Chinese")){
    strArr[i]="Beijing";
  }
}
for(int i=0;i<strArr.length;i++){
  newStr+=strArr[i]+" ";
}

------解决方案--------------------
Java code

    return "I am a Chinese people.".replace("Chinese", "Beijing")；

------解决方案--------------------
Java code

public class Test { 
    
    public static void main(String args[]) {
        
        String s = "I am a Chinese people";
        s = s.replaceAll("Chinese","Beijing");
        System.out.println(s);
    }
}

------解决方案--------------------
String str="I am a Chinese people." ;
String newStr=str.replaceAll("Chinese", "Beijing")

------解决方案--------------------
String str = "I am a Chinese people.";
		String replace = str.replaceAll("Chinese", "Beijing");
		System.out.print(replace);

------解决方案--------------------
探讨

return "I am a Chinese people.".replace("Chinese", "Beijing");


------解决方案--------------------
完整代码:
Java code

public class ChangeString {

    /**
     * @param args
     */
    public static void main(String[] args) {
        System.out.println(ChangeString.method1());

    }
    
    public static String method1(){
         return "I am a Chinese people".replace("Chinese", "Beijing");

    }

}

------解决方案--------------------
楼上说的方法都行。

要注意的是String类里的replaceAll方法参数的字符串用的是正则表达式，不是普通字符串。只不过“Chinese”的正则表达式就是“Chinese”。