FileReader fr = new FileReader("/tmp/etalon.txt");
BufferedReader br = new BufferedReader(fr);
String str;
Map strMap = new LinkedHashMap<String, Integer>();

while ((str=br.readLine())!=null) {
   strMap.put(str, 0);
}

Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
	at java.util.Arrays.copyOfRange(Arrays.java:2694)
	at java.lang.String.<init>(String.java:203)
	at java.io.BufferedReader.readLine(BufferedReader.java:349)
	at java.io.BufferedReader.readLine(BufferedReader.java:382)
	at recct.Appl.main(Appl.java:43)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:606)
	at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120)

String1
String2
String3
....
String100000000

Exception in thread "main" java.lang.OutOfMemoryError: Java heap space

Map strMap = new LinkedHashMap<String, Integer>();

for (int i = 0; i < 100000000; i++) {
    strMap.put("String" + i, 0);
}