Anyone know what this means

Code:
Exception in thread "Thread-4" java.lang.NullPointerException
        at client.method75(client.java:5368)
        at client.method105(client.java:8016)
        at client.method112(client.java:8846)
        at client.method146(client.java:12112)
        at client.method102(client.java:7759)
        at client.method9(client.java:8770)
        at Applet_Sub1.run(Applet_Sub1.java:122)
        at client.run(client.java:4406)
        at java.lang.Thread.run(Unknown Source)